I think its just matter of time. We can tell, not because we are into tech or not-"average person", but because we have seen outputs of these systems enough times as well as actively use it.
AI is in growth phase, and as more people use it more they will be able to tell particularly as they interact first hand with it.
Going back to your original point, people don't hate "slop" because they think it will cost their job (maybe some people). People hate slop, because they are forced to read it most of the day and if you want to do your job well closely babysit, verify and rearrange. The overall expectation of quality has declined over quantity.
I'm not saying its not productivity booster. But the way its used to increase quantity and then map it to productivity. This results in to two things (1) more work for people so worse WLB (2) increased dissatisfaction with work because the quantity is high and maybe you can call it X% productivity boost, but maybe with X/2% productivity boost you may get Y% quality boost, wlb and satisfaction with your work.