I think you're missing my point, which is that the performance range of people with "all four limbs and normal (or above) coordination and muscle capabilities"

I think you're missing my point, which is that the performance range of people with "all four limbs and normal (or above) coordination and muscle capabilities" is at least as great as the performance range of people with diverse injuries. So although it may seem orderly to you in the abstract, it's pointless and arbitrary to organize the paralympics based on type of injury if you're simultaneously allowing a much greater range of abilities to compete in the olympics. If you really care that much about controlling for physical ability, you need to sort people based on some kind of meaningful sport-specific measure which more reliably segregates people's capabilities regardless of age, gender, injury, etc. But injury type (and for that matter gender and age) are extraordinarily poor proxies which in practice often prevent people from competing against their physical peers.