As someone who has mild dyscalculia, this mechanic is painful but I'm happy for the variety. If I screw up, I screw up. I didn't even get we had to use our hp as base on my first run.
I don't think it's hard mechanic, it's more like our brain is turned on active mode during a fight. We're playing, we're pressing buttons, doing rotations and watching out for AoEs and suddenly - stop! Do this math!
It's normal to go "uhh...what?" and mess up even when you know basic math.