Remove awareness and set a breakpoint for tenacity to let you ignore bosses crits, then make all tank busters have the ability to crit which would one shot tanks. Then add str to accessories.

What about certain mechanics that allow tank stances to ignore a detrimental affect? Have tank busters more frequent and more random than predictable which would add a vulnerability debuff that would be ignored when in tank stance. Forces tanks to watch for wind-up

So for example with like Susano EX his Stormsplitter would be more on the random and frequent with the mandatory slashing debuff to force the tank swaps but if you are out of tank stance it would add a vulnerability that would stay on you for a long time.

Make direct hit a dps only stat. Give the other stats heavier weights to tanks, but force them to have to use tenacity to a certain breakpoint.

Set tenacity the breakpoint so high out of tank stance you couldn't achieve it.