Some of both I'm sure, some of which is useful. I think of the difference between free weights vs. free bar vs. machines. Machines teach the smallest number of muscles, while dumbells require all sorts of sub-groups to stabilize. The small movements you do get more practiced, that's the memory, but I think the stamina required is probably leading to development.

I agree there are some insane things out there, and I've seen plenty a non-fit person being taught exercises that only seemed designed to create a dependence on the trainer i.e. they couldn't be done alone and no one else does them. However, what's winning me over is seeing very muscular people signing up to do these things, some of whom I've seen over time improving.