Honestly, who gives a flying fuck if Tia and/or Lyvia get knocked out while fighting.
Increasing survivabilty, uh? Man, talent points, drinking potions and using magic spells are far more important than any weapon or armour.
I can't understand all this damn debate about these battles of yours: it's the least tricky part of the game. More importantly, hunting, collecting herbs/items, making money, farming, eating, sleeping and unlocking picks are more essential activities.
Please don't be so irritated when people discuss stuff you are uninterested in.
Can you win battles with suboptimal RPG build? Sure, this is not a difficult game in terms of harcoreness. Are we still allowed to think about and discuss what build is optimal? Hell yes, we are.
1. The talent bonus to defense is given to leather armor too, not just chainmail.
2. your argument is for why armor is better than naked. not why chain is better than leather.
Tia is LESS tanky with chain than she is with leather.
For example my Tia is level 45 and has 79 defense and 10% evasion while wearing a full suit of leather +2 armor set.
If you were to swap her to a full suit of chainmail +2 and she will instead have... 87 defense and 0% evasion.
each hit deals slightly less damage to her. But she lost her ability to evade 10% of blows (and evaded blow deals 0 damage), instead she will be hit by every single enemy attack.
Overall she takes more damage with this "upgrade" than she would have without it. Especially against stronger opponents. The stronger the opponent the worst this tradeoff is. Since an evasion can nullify infinite damage. While defense is reducing the damage by a fixed amount.
Chainmail simply needs to get rid of that penalty to evasion. Then it would be a very slight marginal improvement over leather.
Although at that point it will still be hideously expensive. at 5 talent points, lategame quest, and a bunch of advanced resources.
Your numbers are off. First, even without armor skill modification base difference between full chainmail and full lether with all iron plates is 9, not 8 (body chainmail has difference 3 with leather, other parts have 2). With armor skill modifications this 9 defence points difference becomes 12 or 13.
E. g. with armor skill 15 and perception skill 10 Tia has 112 defence with 17% evasion in leather armor and 125 defence with 5% in chainmail. This is 12% increase in defernce for 12% reduction in evasion.
Even had defence worked in linear way the build with chainmail would be preferential due to lower variance and thus higher sustainability over crits. But yes I agree that in this case gain from chainmail would be rather marginal (not that you have any difficulty with being able to afford chainmail when you can craft it).
However, defence clearly doesn't work on liner scale, it works on logarithmic. That is when difference between defence and enemy attack reaches certain threshhold the hp loss decreases 2 times (I obviously haven't seen the exact formulae
Chyos uses, but this can be easily proven by several runs). Thus this 12% incerease in defence can easily lead to 2 or even more times decrease in hp loss. Thus having maximal possible defence at least for Tia is an absolute must.
Having said all that, increasing armor for MC and Livia is much more debatable. However, sometimes enemy can overcome Tia's taunting ability, and thus being able to sink a least 2-3 enemy attacks is important for MC and Livia as well.
Since mc sometimes has to fight alone, I am leaning towards thinking that MC too must have chainmail, but yes having to spend 6 more points for MC armor skill is expensive