This is preliminary work. The bigger issue is that this is happening at energy scales that ignore things like gluons.

> Sharper gravitational maps of both the proton’s quarks and its gluons may come in the 2030s when the Electron-Ion Collider, an experiment currently under construction at Brookhaven, will begin operations.

It would be hard to imagine the scientists are ignoring quantum effects since light + proton screams quantum, so it's unclear from the reporting alone if the lack of a quantum gravity theory is enough to make all this not particularly useful or if this is just bad reporting and the experts are confident this is the right way to do things "for reasons". My guess it's probably a mixture because the modelled answer computed from equations and the measured result seem to be aligned.

They are measuring the distribution of energy within the proton. General relativity (GR) describes how a distribution of energy distorts spacetime. They could take these measurements of the proton (if they're complete enough) and compute its tiny effect on the curvature of spacetime with non-quantum GR. Quantum gravity only becomes relevant at the Plank length (~10^-35m) which is still much smaller than the proton radius (~10^-15m) or the resolution of their measurements.