[Perdition]

Currently Turtle Shell feels quite underwhelming in my opinion. Before the parry changes, turtle shell had a niche use on parry characters because their back was their only 'unprotected' area since parries could trigger from side facing attacks. Now they they only trigger from the front, turtle shell will often just not provide any use for you since people are already avoiding attacking you from the front if they know you have a parry and it's very easy to see a sudden surge in crit evade if they try attacking you from the back.

I think turtle shell could provide half of its rear bonus to sides, similar to how it functioned before its nerf, just without it affecting the front this time.

[Snake]

I'd rather increase the resistances from the back rather than return it to what silly meta heavy armor it was before.

Doubling Armor values when being attacked from behind can also be funny and a silly way to counter those backstabbing spies.

[Perdition]

The issue is the bonuses being tied solely to the back is why it's trash now. Old Turtle Shell applied to literally every direction, but halving the effect for the sides and then having it be normal for the back should be fine. By having it apply to the back only, people will just attack your sides and now your 10 star item is useless. It's also really easy to attack specific sides of a character with all the options to both move and attack, or low momentum movement. And against VAs which are really the only class that wants to backstab, frankly, turtle shell doesn't do anything.