When I lift weights and do a squat, my ankle mobility limits me. If I wear lifting shoes with a bit of a heel on them, I bypass that limitation and can more efficiently work my legs, back, etc, the actual focus of the lift. I might still work ankle mobility with other exercises, but not while squatting.

Calculators get past the arithmetic (ankle mobility) quickly so that the real target, the problem with new, higher level math concepts (big muscle groups), are the focus. Arithmetic skills can still be drilled elsewhere as needed.

Whereas LLMs to write essays can be like not doing the squats at all and just hooking a motor up to move the bar up and down. No low level skills drilling and no targeting high level concept gains achieved.