Slots are great as long as you stick to unaltered human scale. A dungeon crawl, secret agents, etc. Try to do mutants or supers or vehicles or mecha and the cracks really start to show. It becomes a real nuisance converting one scale to the other, etc.
Also you know how much a thing weighs, but wading through the many different interpretations of slots to figure out whether your character can sprint while hold a mini-fridge full of kobold cutlets over their head is a drag.
Yeah, if it's like "This game has pixies and giants, we're doing fucking weights", I will nod and say "Okay, fair enough, then."
Caves of Qud is the perfect example of why what you're saying is super important. Caves at least has the benefit of being a video game that handles it, but having some characters have slots for front and back feet, anywhere between 0-4 arms, no torso sometimes, or two heads (and two faces) is a lot!