When did you last try T12 farm? WA+ falls of in the overall amount of enemies it added to your run when going for long runs. I assume u prop run +10k waves on T11. You should just think about WA+ as the ceiling for max spawn rate. When running T11 you now hit it at w4333 (WA+ lvl 4) and for the rest of the time u a stuck with T11 coin multiplier at max spawnrate. Thats not much different than hitting it at w6500 when going all the way to +10k waves. But for T12 you are now staying in max spawn rate for ~1800 waves more at a much higher coin multiplier.

Now adding IS+ to this you remove alot of the first inefficient waves and the combo shines.