Phys res is also good if and only if you can stack it sufficiently high.
And while stacking physical res is mostly available only for physical builds (melee and casters), stacking armour is available for literally everyone.
DA is meant to save you from crits, in first place. It’s much easier to get 3k+ DA and be crit-immune, than get an extra 40% phys res to mitigate crit.
Very few casting sets offer armor. Very few classes offer significant armor boosts.
What is your definition of “high armor?”
Dont use those shitty sets then (unless they provide really great compensation). Use sets with high armour (Light’s Defender, Justice, etc) or green items with high armour and armour bonus. And class bonuses are irrelevant. You can get 3k+ armour without any bonuses to armour from your classes.
3k+ is quite high for me. Obviously, you can never have enough armour…
May I ask which caster sets offer high armor? Light’s defender is possibly the only one I know of
true
Most casters sets didn’t offer lots of armor. Hey look cold Drain Essence Apostate with Chillwhisper set. Both no physical resistance and armor…
The life and times of cold casters
lvl109 Alex has effective 2.9k OA. Unless you have heavy OA shred on top, 3k DA won’t make you crit immune. This number must be significantly higher.
Enemies like father kymon can also shred your DA by ~400
Sure, but in Crucible, you get DA bonus, no? And crits are dangerous only with “deadly” mod, that reduces enemy OA. “normal” 1.3 times crit wont make a big difference. BTW, you can dodge meteor, it isnt neccessary to facetank it. After all, Alex can also reduce all your resists by a large value, including physical resist. Sure, good builds can facetank it, but there is no shame to press disengage button at the time you see meteor falling and be safe.
You don’t get DA, unless you use Ulzuin buff. But standard run is the other 3 buffs+banner.
None at all. But I was geting one-shotted from 15k by all manners of crap like Kymon’s leap, Theodin’s aether dunk, Iron Maiden’s Blitz, Reaper’s autoattack, etc. on builds that never had such problems before with half the stats. And btw I did survive Meteors, if very occasionally, on the same toon. Total rng. But that’s not my point.
It’s easy to generalize if you only play SR/Justice/Cyclone cookie cutters. These sets are oupie defensively. Thing is anything not op defensively dies from a sneeze now.
Seriously, I think enemy all resist reduction should not include phys res. And specific phys rr should be added in reasonable values to specific enemies. Then, phys res on top sets should be adjusted (accordingly) like 19% on Cyclone? Wtf. No wonder people don’t play anything else. Phys res at at least 30% is like capping res these days. You gotta have it or you’re inadequate.
You are exaggerating…again.
I think most of my builds don´t have more than 2.500/2.600 Armor and less than 30 % Physical Resistance. And they don´t die at every sneeze.
Which shows exactly what you play. 2.6k armor and about 30% is on a dmg focused build is STRICTLY TOP TIER, man. Most builds do not even have 2k armor and struggle to get 15% phys res. Most builds in the game. Not most builds in the forum.
Bloodrager got 12% phys res on the set AND 65+6% da AND 700+6% health AND double res on every piece. It’s a VERY tanky set compared to the average. One of the most top tier sets in the game (even after the nerfs). I’m talking about the NON-TOP-TIER builds. Radaggan, Runebinder, Rimetongue (that was on one of the best dw melee builds once - John_Smith’s N&O), even freaking Venomblade (that was said to be one of the best sets ever and now is just CRAP), etc. Or non-set builds. Or gimmicky/creative builds. Or blue sets like my all-time favororite Silver Sentinel. You play them lately? They are hardly playable anymore. Sure you can clear crucible with them (eventually). But you’ll die a lot, get one-shotted by everything, can’t dream of SR beyond 65, get frustrated, see that times are crap on everything despite the squishiness, rage quit, etc. No reason for anyone to ever play anything but top tiers.
If you think I’m exaggerating take a peak in the trading thread and see what people are looking for. Same pieces to same top-tier sets, EVERYONE. Or they stop trading because once you get SR set you really can’t get any better in Grim Dawn. Constant nerfs to masteries instead of gear and heavy environment buffs are changing GD from the aRPG praised for stunning diversity to a game of a handful of playable builds and tons of trash.
Some builds definitely have lower values, it all depends on the boots. 
I took a look at your Dervish and if you had chosen (just as an example) Sailor´s Guide instead of Eel (and skipped 5 % Crit from Torch) you would have 3 % more Physical Resistance. Much? No, but a start.
You are right that Dervish (or better: The Masteries) lack a certain amount of defense. You only got the DA from Consecration/Shadow Dance and the CD of Resilience is too long to really invest many points in it. My Dervish didn´t survive well, too…because of this reasons.
Blue Sets/Blue items get an overhaul with 1.1.5.0. Adoomgod is collecting feedback for a lot of items to make them better and open up more build diversity.
I always went for Sailor but since Egellon slow res is no longer such an issue. Eel has 2% dodge/deflect, bunch of da and pierce res which is more useful than the res from Sailor so it’s not such s downgrade. Sailor got that sweet freeze res though… but I’d have to give up not on 5% crit from Torch (I didn’t take the 3rd) but 5% oa. This is too much.
Ofc I could drop Merciless and pump up Dual Blades. Or drop Fervor to 16/16. Or give up on maxed ABB. And I probably would do one of those if DB gave 1% phys res for 1p beyond 5/16 or at least gave some acid dmg. But as is the defensive gains to offensive losses are too little.
And it’s not that now VB pays for dmg with increased difficulty - as it used to. I pilot VB pretty well and honestly it is close to impossible now to clear 170 without Courageous Tincture, greens or Aeon. I also played a couple of Runebinder setups lately. And Silver Sentinels. Same thing. Then I decided to screw that and made an SR set dervish. Conclusion: no reason to play anything else. It’s not a good trend, imo. And even if I’m exaggerating that’s how I feel, and that’s not irrelevant how players feel.
I took this: https://www.grimtools.com/calc/a2E4dM7N and you still get the OA.
As for Blue Sets:
I don´t mind blue items (my Trickster uses 2 of them). But strictly speaking, they are no Endgame-Sets.
That DB doesn´t give enough bang for the bucks…well, I said that when the change was made.
So, am i inadequate with my AAR build? It has ~10% phys res and feels OK due to armour and flat absorb. And it doesnt uses sets you’ve mentioned. Phys res isnt as great as you claim. And i;m fine with that. If you make phys res better (remove phys res reduction, etc), there would be too large gap between builds, who get phys res for free, and all others.
Veil of shadow reduces enemy OA, which is the same as adding DA to yourself, no?
Yes, almost. OA shred is not multiplied by +x% DA so flat DA is economically better. +10 DA translates to +11 DA when you got +10% DA from gear and devos. -10 OA shred is always -10 OA shred. (However, -x OA shred reduces the efficiency of enemy +x% OA bonuses but these are rare.)
Also, the PTH formula and the resulting values such as crit chance and crit multiplier or total dmg multiplier (this only kicks in when oa-da difference is huge) are dependent not only on the difference between DA and enemy OA but also on the level these values are at. Uhh… I mean… 3k DA with 2.5k enemy OA is not exactly the same as 2.5k DA with 2k enemy OA. Close enough though. The exact formula is in the official Game Guide.
But it has… let me count… 6 rare affixes. I know you put some magic affixes there too but Thunderstruck Alex pants of Kings is like 2-3 drops in 100,000. Such items don’t really exist in a legit game. So such builds (in my very humble opinion) should not be a part of a balance discussion.
Besides, All resistance overcaps are 60+% so you almost never go below 80%, armor is 3+k, you got 440 flat absorb most of the time on top of 21% absorb and 18% dmg redux. This hardly disproves my claim that phys res got too essential to be attainable TO AVERAGE BUILDS.
What’s wrong with an item with 1 rare affix? Those arent hard to get at all. Rather, they’re standard items in endgame - you dont even pick up yellows there.
About pants - that was just my luck. I indeed got that double-rare in legit way (despite your claim). And no, this build doesnt requires that double-rare combination. 1 rare affix with stun res is enough. I might lose ~4% DPS, but that’s not critical, considering i dont even have Glyph of the Storm witch, that boosts DPS far better. On other hand, my boots and weapon has absolutely useless prefixes, and my offhand has ~30 itemlevel. Not counting sub-optimal mods on many items. And still i have 50+ all res overcaps and 3.3k armour (GT doesnt count crafted armour bonuses and above-average %armour rolls) And i made those videos even without one great unique ring for that build (which means DPS loss).
And 25% damage absorb on top of that 50% of the time…
But why do you think, that average build would feel tanky only with 20-30% extra physical res? He might be tanky VS some enemies like Reaper or Kupacabra, but others would still crush him. Physical res wont help much VS physical shotguns, for example
To add to this, this is where things like reliable DA shred comes in very handy. I.e. SBoE