All right, we have fossil skeletons or partial skeletons of animals that were that big... do we toss out the Square Cube Law to make them weigh less as you suggested?
My point is that we have "Laws" in conflict with the observed facts. Something has to give. Either way, there are cosmological implications that will be impacted.
The square cube law does not state that larger objects are more massive than smaller objects. The problem of weight arises if we reconstruct large dinosaurs on the assumption that they are simply scaled up without any structural compensations. That is equivalent to scaling up a model airplane or model car without adjusting the thickness of the structural members.
Now I have said I don't have a solution to the weight problem. I think, however, that conjecture would more reasonably start with scaling of components rather than by assuming Newton and Einstein are wrong.