as soon as bodies clash in sparring it's broken up....because you can't see the points being scored. and if you can only use a subset of techniques, then what is that? it's sparring that may or may not happen to have overlap to principals found in kata...but the mindset is sparring.
I'd never heel palm someone under the chin during sparring...thats just being rude and they might get hurt by biting their tounge, shatter some teeth or give whiplash ouchies...thats not very nice or sportsman like. (imagine that sentence as the voice of 'churchlady' from SNL)
just a different frame of mind, range, and 'game' (keyword).
not only that, but for all of the applications you find/practice in kata, do you also practice counters for? like a defense against tora guchi and ridge hand strikes? those counters...are they found in the same kata?
why not? and how likely is it that one kata would have defenses from another kata's attacks?
Maybe kata was originally designed with both attack and counters and was used for training many people a skillset(pretty useful in T'ang dynasty H2H armies)... but gradually was changed and customized to civillian self-defense with the assumption the attacker is the less skilled bad-guy? which also fits why Okinawans were very careful who they taught stuff to. fight against someone with the same set of techniques and it just comes down to physical endurance and speed...not good odds for a SD system.
kata techniques in it's present form isn't for using against itself. sure you can make stuff up and say it's based on it's principals of movement...you could even pick out parts of another kata where the defense against a defense looks similar and convincing. what I'm saying is, a single kata does not have all the defenses, and counters to its own defenses. thats why kata is not for combat (unless you've studied with someone with THE lost kata up on a mountain somewhere), it's an uneven SD system. the assumption is an aggressor not an equally matched opponent. in my opinion anyway.