[RightWhale]

either GR or QM is right while the other is wrong

They are both right, and both are incomplete. It's a problem for cosmologists especially in the inflation model, but until technology advances further it is not a practical problem.

[Southack]

"They are both right, and both are incomplete."

No, they are specifically *not* both right.

General Relativity was wrong when it had the Cosmological Constant (i.e. a static, non-expanding universe), and it is wrong today without it. It still fails to predict orbital positions, for instance, and it is soundly refuted by the energy and Gravity realities of Quantum Mechanics.

Quantum Mechanics may or may not be incomplete, but at least it doesn't have General Relativity's glaring flaws.