From me it’s going to be biased since I’m far, far from exhausting every possible build idea, but among the dozens of characters I’ve created, I’d say the one character that might be able to continue to get through ultimate if I tried just putting gear on him that I find in the regular shops (not even faction revered) is my shield-donning cadence witchblade.
One of the main reasons: he does 1128-1656 flat physical damage independent of a weapon from deadly momentum at 14/12 (and 12/12 is not bad either if I had no +soldier or no +deadly momentum items equipped). It’s like if he could just punch with his fist, even his fist would be doing tons of damage.
That means even with the shittiest weapons in the entire game (like something I stashed when I was level 1), with all the physical modifiers he gets from devotions on top of additional flat damage from shield training and menhir’s bulwark, he’s easily going to be dishing out 20k+ DPS even with the worst gear imaginable (maybe just something yellow of alacrity would help – attack speed helps a ton with so much damage coming independently of the weapon damage). Combined with the physical resistance debuff from CoF, that’s enough to plow through everything ultimate has to offer (Nemesis might be a bit of a challenge).
So that covers the damage output in a totally gear-independent kind of way (well, at least as much as I think one can get in terms of gear independence in this game). In terms of survivality, with shield training, bulwark, and overguard, he’s not going to be very squishy even with crap armor and shield provided his resistances aren’t crap (which is easy enough to cover even with gear bought from the non-faction vendors in Devil’s Crossing and some components and augments – and focusing on resistances is a requirement for all builds anyway). Even in some hypothetical scenario where it becomes too difficult to facetank without better gear, he can just as easily switch to crap pistol and board and do respectable damage.
The most gear-dependent builds which would end up feeling hopelessly underpowered that I created if I did the same thing (just took off all their gear and only used what I can buy from an ordinary store) are my casters (ex: my CT sorceress) and my nightblade dual-wielders (saboteur, trickster, blademaster).
The only one on my end that I feel comes close to my cadence witchblade in gear independence is my poison-based witch hunter, but I’d lose two of my primary attacks if I lost my gear (DAS and DIG) and would have to resort to spamming DEE and kiting like mad. The only reason he might be viable is that his poison damage output is pretty high independent of gear and, because it’s poison, he can just tag the enemies and run around like a headless chicken without taking many hits.
Retaliation warder (another one using shield) might be viable with eclectic gear but the retaliation damage just from devotions like Messenger of War alone don’t suffice in ultimate difficulty IMO if you don’t want to go insane waiting for stuff to die (actually I do that anyway even though I’m dealing over 10k retaliation with a lot of eclectic retaliation gear). There boredom might trump viability.
2H melee warder is medium in terms of gear-dependence to me. The lack of a board starts becoming apparent to me a lot with that one when I don’t give him the best armor and weapons and accessories I can find where he ends up dying faster than his Wendigo Totem can heal him in some instances even with massive HP. Even though he has almost double the HP of my witchblade, it feels like he’s squishier and especially without very good gear (though he never felt the slightest bit squishy until I got to ultimate and died in the blink of an eye even with Wendigo up in act 1 of all places).
In terms of what people often seek when they want gear independence (like a first character to clear ultimate without too much struggle and farm better gear for other builds), the cadence witchblade fits the requirements better than any build I’ve personally tried, and I tried a lot before I discovered him. I kept creating casters thinking they’d be the least gear-dependent builds in the game, thinking they’d be obliterating stuff reasonably well even if they ran around naked – I shied away from cadence for a long time because I wanted more AoE and this every-third-strike hit thing felt weird at first. I haven’t given any pet builds a very fair chance – they bore me a bit too much and the idea of having to keep track of which pet is still alive sounds stressful in the heat of battle.