Do you think "This needs to be viable, non-breaking and costed appropriately for Solars, Abyssals, Infernals, Lunars, Sidereals, Alchemicals, Dragon-Blooded, raksha, spirits and first circle demons." is a reasonable thing to ask your game developer or GM to do? If so, why?
Do I? That's a good question! Are you actually interested in hearing an answer or are you just trying to get a soundbite?
It's all right, I'm going to assume the former.
So, here's how it works. "Viable, non-breaking and costed appropriately for Solars, Abyssals, Infernals, Lunars, Sidereals, Alchemicals, Dragon-Blooded, raksha, spirits and first circle demons" is not actually a binary - it's a
spectrum. Things can be more or less viable, more or less non-breaking, more or less appropriately costed.
The further you are to the wrong side of the spectrum, the worse the product is on these specific factors. The closer you are to the right side of the spectrum, the more effort-intensive your product is.
But, uh, here's the thing.
You get something out of this. There is an actual product which adds richness to the gameplay, provides player enjoyment and so on.
So, you strike the balance. You assess how much work you can expand, and you move the slider on the best spot you can get on that spectrum.
That does indeed mean that your product will not be
entirely "viable, non-breaking and costed etc." Some stuff will be too expensive for a Solar, some stuff will be overpowered in the hands of a Dragon-Blood. This may have a negative impact on the game. You do in fact want your product to be as balanced for cross-splat compatibility as it can be given the effort you can allocate.
As long as the benefits surpass these drawbacks, the end product is fine. Some people will complain that if you have this one Charm interact with this other Charm it will cause an unbalanced interaction, but as long as enough people have an improved experience from it it's omelette and broken eggs.
Stuff you can do to move the slider closer to the right end of the spectrum:
1) Have Charms grant special benefits to the most powerful (or MA-focused) Exalted splats.
2) Restrict the full power of certain Charms to the least powerful (or least MA-focused) splats.
3) Don't give MA access to first circle demons as a general rule.
4) Restrict MA access to spirits of the right category or power.
Ex3 is doing at least the first two, I don't know about the others. Those are ways in which you can improve the unbalance inherent to cross-splat access to martial arts.
And honestly, I get not liking martial arts. If they do nothing for you then they represent a net loss to the game, from your point of view. The important thing is to keep in mind that the game is trying to reach a certain audience, and that audience has historically been highly receptive to martial arts as implemented, so... It's not bad
design.