When Moffat discussed other alternative graitational theories and the problems in them, he wrote this regarding "quantum gravity", an attempt to combine gravitational theory with quantum theory: (John W. Moffat, "Reinventing Gravity", Harper Collins, 2008, page 142)
Some theorists simply claim that since gravity is observed and quantum mechanical effects are also observed that qualifies as enough experimental evidence that a quantum gravity theory is necessary.
The implication is that quantum gravity is not necessary. The problem with getting quantum gravity to work is to take any theory that works on the quantum level and getting predictable results that match what is observed about gravitation on the cosmic level.
If one doesn't need quantum gravity then there is no need for a "graviton", a quantum particle of force associated with gravitation like the photon is associated with electromagnetic radiation which so far has not been detected.