I agree with Glythe with the response to this, dps builds or literally just using a modded extra skin already trivialised lower level content, including the Qatik dailies. I think armour chipping is a good solution though, it all just depends on the numbers picked for how it's balanced and I think it can be done correctly. In my opinion lower level content should still be easy for a high level to do and it wouldn't make sense to me if armour chipping makes it impossible for tank builds to do, while dps builds could still easily blow through it. The doubling of elite hp should make it harder for everyone though and I'm not sure I would be able to solo dc anymore with my dps build considering nimble shoes were also nerfed. I expect animal handling builds and maybe bc builds would probably still be able to do it though.
I don't think mob damage does actually scale linearly, despite what Citan says, because stuff like trolls, minotaurs, worgs and worghests can apply debuffs which multiply their damage to you. This is why the first floor of winter nexus can be deadly to almost everyone, even full yellow max-enchanted level 80s. Also from Citan's own numbers it's not quite a linear scaling since the rate of damage increase does change, but only slightly.
Every mob also has crits which multiply their damage. Crits are very noticeable with elites both due to their higher crit rate and higher base damage. Sometimes you can get some ridiculous things happening, I remember being hit for 500 by a wintertide troll in my tank set, which was through 38% physical mitigation from unarmed and I think the 27% mitigation from bulwark mode, but there's a bug where it can disable if you use/drop an item which might have happened. I think my shield team mitigation and headbutt mitigation were both down (and I was stunned so couldn't reapply them) and I don't think I had any stacks of shield forcefields, but I was at max armour, ~900 with the shield thick armour mod. This is just what happens when you get a rage critical when you're already knocked down since the multipliers push the damage up to crazy amounts. I honestly think it's mostly fine, this was the highest hit I've ever taken in probably at least 15 runs and it was only a one off. However, I'm pretty sure the minotaur rage attack in wintertide is a 1 shot on any player without mitigation. It seems to be bugged and counted as burst damage though, which means you can evade it with nimble shoes.
I really appreciate the power regen on bulwark mode in wintertide especially. The frost hippogriffs have a dot which lowers your power and without the power regen on bulwark mode you can be completely drained of power even just pulling 1 or 2 of them. The power regen here becomes absolutely critical because otherwise I wouldn't be able to use any abilities at all. It's also important for keeping up pulls and with dots keeping you in combat seemingly forever, you would have a lot more standing around which isn't fun and from my experience, people in your group will get bored and start pulling mobs themselves. I also imagine it's practically required if you want to use metal armour, but personally I think metal armour is never worth it with the current state of the game. I wouldn't mind seeing it reworked if the easy infinite flying is seen as an issue however.
Again, agree with Glythe's response here. Other builds are already capable of doing this, so if anything it just brings tank skills up to par with the other skills. Sword/psych reducing mob damage by 50%, while having high damage and utility of a mez at any point makes them a joke, but so too does simply kiting with a ranged dps skill like fire magic or archery against melee mobs. Animal handling is also insanely strong and I've seen pets solo fr elites on their own. Staff has probably actually been nerfed slightly in this regard, it used to be able to solo any enemy in the game pretty much. You can just look at Space's fire/staff build or Professorcat's staff/druid builds and see what they've achieved with them. I'm not sure that staff could solo the FR elementals anymore but I would be happy to be proved wrong.
I also think the balance in itself is how long it takes, especially with bulwark mode, it takes absolutely forever to kill even just a single elite if you're using a tank build. I've said this before as well, but I really don't think elite soloing is a big issue, you get the same loot whether you kill it with 6 people or just 1 person and there's no special thing you can abuse in order to somehow get a lot of money or exp from doing it. That being said I wouldn't be against all elites receiving a SLIGHT passive regen that although might not stop you from soloing them, would just make it even longer if you're using a tank skill especially.
I was aware it was a separate multiplier, but I did not realise it was applied before the flat mitigation. This explains why I'm actually able to tank the fire/cold stuff despite only having the shield mitigation against them.
That was my assumption too, perhaps I was wrong then in my post earlier.
I would be worried about nerfing bulwark mode too, it's already the main mod-free mitigation provided in shield and therefore a crux of many players who don't have their mods perfectly rolled, which I believe was the biggest issue with tanking before. You also can't forget the -50% damage penalty it comes with, which if you compare it to something like unarmed, which gets 38% passive physical resistance, 53% darkness and psychic as well as 42% acid, nature and poison which actually all turn into damage buffs for the skill, I'm not convinced nerfing bulwark mode is the answer. I also think the ability to tank the fire/cold mobs in wintertide might actually become too difficult again since there's such a reliance on only bulwark mode and elemental ward in order to prevent their damage. Also, although the numbers on unarmed might sound crazy, wintertide is actually still a difficult dungeon to tank even with all of them stacked. Now imagine you don't have every mod and consider that Citan wants to double elite hp and honestly I'm not sure a nerf is necessary. I will say that GK and below becomes somewhat trivial, but armour chipping should be the solution to that so I'm not worried about it.