I agree the label should be changed to something users actually understand. Even if “trainer difficulty” is technically accurate (I don’t think it is), it’s not a good label if users don’t get it.
“Gradient simulation” might be better, as “off”/“none” and “100%”/“max” make more sense in that context.
I do think Graidient Simulation is probably the best (my opinion) the first 2 options could still confuse many and if Gradient Simulation confuses then they should remove themselves from Zwift.