Slightly simpler version:
Step 1:
Put full str values on tank accs along WITH the vit.

Step 2:
Nerf every tanks potencies a little to compensate for the sudden boost in damage.

Fixes player issue: Tanks scaling 'appropriately' in the long term.
Fixes Dev stated issue: Str and Vit being separate so they can adjust the values of defense and offense as needed in the future to maintain encounter balance.