GR explains (adequately) big things like galaxies and QM (adequately) explains tiny things like protons.
That's chalk and cheese.
Except gravitation, in general. That's where they contradict each other; One theory explains gravitation as the curvature of spacetime, while the other explains gravitation/gravity (the 4th fundamental interaction/force) as the result of the particle graviton. Of course, should the graviton be discovered by any physical means, the existence of the force of gravity (something RE'ers love so much) will be evident.
The inconsistencies in Flat Earth Theory are all about the same things:
1. The shape of The Earth: is it a coin or an infinite plane?
2. "Gravity": is it real or is it an illusion caused by "The Universal Acceleration"?
3. Light: does it bend or does it not bend?
Those kinds of inconsistencies dwarf the issue of GR not marrying up perfectly with QM.
1. It could be either, but we can't tell which of them is correct in our frame of reference.
2. "gravity" is basically us undergoing proper acceleration, in RE or FE.
3. I think the majority of FE'ers believe that light does bend.
Of course, these "inconsistencies" are nothing compared to the contradiction between the two most dominant theories in modern physics. That's my point.