Is it Viable to have a class that is say Full Arcanist, or Full Demo. I’m interested because I simply think it would be fun to have access to more skills and specialise in a single area more.
The reason I’m concerned it’s no viable is because you lose a potential 50! stat points. If you do no get some stat points is it simply not viable? I guess one could always just pick a second class and not use skills…
Appreciate your replies.
I haven’t tried it, but I do think it’s “viable”… there’s just not much reason to do so with the sweet synergies this game brings. As an Arcanist you’d probably end up being an extremely squishy character.
If I went pure anything I’d go pure soldier since there never seems to be enough points to use all those sweet defensive skills. Soldier is so well-rounded that it wouldn’t need a second mastery to cover any weaknesses. Even then I wouldn’t be able to resist tapping into Shaman for 40% health haha.
People have shown that it is viable on multiple threads on this forum but then the argument starts about going pure versus multi classing. You can definitely go pure but you are just gimping yourself needlessly. I’m definitely in the two class camp like 99% of the experienced players in this forum. There is no reason not to except your own personal desires 
Soldier seems to be the only mastery with enough fantastic abilities that it might make sense not to diversify. It’s really hard to justify even for soldier, though. 26 points in shaman gets you +40% health. 17 points in demo gets you 144 OA, + 21 fire damage, and + ~100% fire/burn/lightning damage. After 50 points in one mastery, you’ve got 170 points to spend. How likely is it that after 150 points spent, you’ve got something better than flame touched?
Viable, no through Ultimate? No, though it is possible.
Viable through Veteran? Yes, and you would be perfectly strong.
Your stats, and missing synergies will make it hard past Veteran, and very hard in Ultimate. That isn’t to say it’s not possible, just that it isn’t a viable option.
So It can’t be done on ultimate or is very difficult?
It can be done but it is very gear dependent and you pretty much have to go defensive on your devotion tree.
The real ? you should be asking is why would you want to go pure Arcanist when most of the other tress have really great passives, aura’s defensive abilities really early in their trees.
Take for example putting 5 points into Nightblade mastery and 12 points in Pneumatic Burst gives you a great heal.
Or going 5 points in soldier mastery and 10 points in Military Conditioning will grant you 20% Health and 18% Physique.
Demolitionist has skills like Vindictive Flame, Flamed Touch, High Potency and Flash Bang all very early in the tree.
It all depends on what you’re trying to build. The thing pure Arcanist has going for it is that you’re looking at more nukes. You can get Callidor’s, OFF and Sky Shards all at once, plus IEE, Maiven’s and passives. Stick some good devotions in there and you’re looking at a massive DPS machine. I have an Arcanist in Elite purely for build experimentation purposes and it absolutely destroys everything even with yellow store-bought gear.
Ultimate is definitely doable with a solo mastery class, I have an Occultist summoner who basically just runs through BoC. You need to have a fairly good working knowledge of affixes, components, gear and augments to make it, though. That character is sitting on 11k HP and 60% and higher on all relevant resists with just 25 physique, for example.
It’s actually very easy with Occultist because as far as Occultist goes extra skill points = survivability, thanks to skills like Storm Spirit, the BoD line and Possession. With all the skill points you need to level the familiar, the hellhound, and summon support skills you have just enough extra skill points for 1 other skill line. Survivability is not an issue with end-game gear, so what I needed was a nuke/control skill that worked well despite my middling OA. Rather conveniently, that’s what Bloody Pox is - especially if you pair it with a devotion proc like Eldritch Fire.
I saw no reason to pick a second mastery with that build.
Edit:
I’m not sure what people mean by lack of synergy because each mastery was designed so that skills within each mastery had synergy with each other. You’re giving up these synergies if you pick skills from another mastery, so the net gain is zero.
If you only take CoF from Occultist, for example, then you’re basically giving up CoF’s synergy with summon skills and nukes like DEE. But why does that matter if your goal is to make an melee elemental damage build? The only thing that matters is what you’re trying to accomplish.
It’s possible (so technically viable), but I wouldn’t say a desired path by any means. It seems everyone is already in agreement with this assessment.
On another note: I did reach Act3 Ultimate on my 100% demo. Could’ve gone further - it wasn’t ‘too’ bad.