Mystic fixes?

[Man_Over_Game]

No, that's because the core thing the Monk does is unarmed attacks and so they get the Martial Arts feature. They have Ki points to spend on abilities, but they don't need to do that to still hit their niche of being an unarmed fighter that attacks more than average.

Ripping a mechanic out of one class and using it as a mechanic for a completely different ability set for subclasses across all other classes... to be honest sounds a bit weird and smacks more of homebrew than 5e design. At that point Ki might as well be called Psi points and the Monk gets to use them for other things. And why would the Monk be the original Psion class? The fluff of Ki in 5e links it directly to the body and physical acts, not the mind.

If you're going to give points to subclasses why wouldn't you just retain the core Mystic class and then give the subclasses a smaller pool of Psi points to use alas full casters and their 3rd caster subclass counter parts? A core Psion class is important because how many people would want to play a Psion, then get stuck with a bunch of stuff they don't want because in order to get psionics they need an irrelevant to concept main class? If I wanted to play a Psionicist and got stuck with a bunch of full caster slots and spells it would lead to 1)power balancing issues and 2) a disjointed sense of character identity. Why can I cast spells better than I can use Psionics? And no, refluffing spells as psionics isn't adequate to make that go away.

I'd say that the Monk's unique identity comes more from his mobility and versatility. Bonus Action attacking is something everyone can find a way to do it. The fists themselves don't really change much in terms of playstyle, decision or niche.

We've copied mechanics from one class to put on anothe, even more than once. Eldritch Knight, Martial Adept, Bladesinging is basically Barbarian Rage, tons of subclasses explicitly mention a spell when they otherwise wouldn't cast spells.

The idea is to give everyone the means of making the Psion the way they envisioned it. They tried the method of having one class do everything. I'd think it makes sense to have each class have an option of doing their thing...psionically.

If a Psionic Wizard had a feature that said his spellbook was his mind, his Psychic, Thunder and Bludgeoning damage was increased, and he no longer needed nonexpended components, would he be all that different, thematically, from anyone that wanted "Psion that uses mind-powers"?