Evasion and protection break point in Legend of Grimrock
Solution 1:
It completely depends on the enemies you're fighting and the damage their attacks do.
If you are fighting an ogre, and they will hit you on average for 70 HP damage, and you have 30 protection, you'll only take 40 damage. If you have 50 evasion, let's say for argument's sake that it's a straight-up percentage of hits dodged, you'll take 35 HP damage on average (i.e. 1 out of every 2 70 HP hits.)
If you're only fighting spiders, and they hit ~15 HP, if you have 15+ protection you won't take any hits, but your evasion points will be worth less.
So, basically, the bigger the enemy, the more worthwhile evasion is. ... but watch out when you get hit.
Solution 2:
For your front line fighters, tanking isn't worthwhile in this game because Evasion is vastly superior in my opinion. It would be much better to wear normal cloth armour until you get Light proficiency, keeping your evasion up and gaining the + Protection, don't go toe-to-toe with enemies, back away or circle strafe. Not getting hit is key in this game.
Even so, your front line fighters would ideally have good dexterity and the evasive trait so they can effectively protect the back row, negating damage is better than soaking it up. If you really want a Tank, just have the one, because he'll/she'll be receiving a lot of damage, especially on Hard mode.
Hope that gives an idea for your dilemma. Someone could probably give a much better answer than I. :)