As far as I know the way armor works is:
- below LEVEL x 10 armor you have 1% mitigation
- the first 10 above that gives 10% total
- each subsequent point gives 0.5% extra
This means that extra 10 armor is nice to have but not very good at low mitigations(80 damage taken vs 75 isn't much of a difference). At very high levels it'll change damage taken from mildly annoying to insignificant. At the titan fight my warrior had 98% mitigation, without thick skin it'd have been 93% for a 3.5 fold increase in damage. Those 3-4K swings were actually healing him thanks to leech.
Thick skin is really, really good since man-at-arms will be immune to everything except tenebrium and physical. You can easily get 60%+ tenebrium resistance and that damage type is very rarely noticeable, TS ups your mitigation by a significant chunk to the only thing that could actually kill you. I think it's picture of health and hp from con that are actually useless, had 1280 hp on the warrior at lvl22 but he didn't take more than 500 damage in any single fight. More hp is also much worse than high mitigation when you look at spells like regen and mass heal.
For a general feel of how effective armor will be, at level 20 my warrior had 78% mitigation with leadership and thick skin/3 armor specialist(without fortify, potion or defensive stance). That's still 78 with the common buffs rage and fortify, so thick skin ups effective hp by 23%.
