Intel loves performance, because people want performance. Complexity is the cost of increased performance. As an example, I would guess that of the ~2000 pages of the instruction set reference, at a minimum 1000 pages document the various SIMD instructions. You don't need those, or the floating point operations, or SHA instructions, but I don't see any harm done by making them available.
I think the single instruction which can do the entire job without any magic assist is subneg x, y, z:
Subtract location x from location y; store the result in location y; and branch to location z if result is less than 0; else proceed to next.
Or various trivial variations of the same idea.
Any complication beyond this is no more than syntactical sugar and performance optimization.
If you focus only on direct memory addressing (no indirect or indexed), mine does still work, but mov doesn't. I think.
It's just some CPU instructions!
Maybe they aren't doing a good job of describing them succinctly?
These things aren't written to be brief, they are written to be complete.