It'll take either the next Einstein or some groundbreaking experimental observation to get there in my opinion.

If it was possible to incrementally fix these theories, the army of postdocs working on these would have already done so in the last decade or so.

There are ways of adapting MOND to match general relativity, should it turn to be correct at explaining what it is supposed to explain (like the movement of galaxies).

Galaxies are typically so far away from another they're almost like point sources to each other, hence Newtonian gravity explains their motion very well.

However, inside galaxies things do not behave as expected, as stars in almost all the galaxies we've measured does not move like Newtonian (nor GR) behaves based on the matter in the galaxy we see. One alternative to the mainstream theories of dark matter is to modify Newtonian gravity, called MOND.

This work tested if MOND fit the motion of galaxies in galaxy clusters. They found it did not.

MOND already does not explain other phenomena that dark matter can so it's not terribly surprising. Here[1] is a nice accessible talk going through all the evidence for dark matter.

But it is technically a possibility that there's two things are going on, something MOND-like as well as dark matter, so worth checking.

[1]: https://pirsa.org/26030070

The test here is for the inverse square law of gravity. The rival theory in this case isn't GR, but MOND: https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics