Radical thought...remove the off-tank?

[Nezerius]

Weakness only lowers sTR, DEX, INT, and MND by 25%.Strength now - MP and HP are no longer affected.

Which doesn't really disprove his point. 25% lower STR still makes the tank weaker, due to the fact that they'd be doing less damage.

Whether it's a big deal or not being beside the point. I personally don't think it is, since the offtank can just shirk and help the main tank getting an enmity lead.