The square cube law does indeed state that larger objects that are identically proportionally constructed of the same materials will actually be more massive... more massive by the cube of the size multiplier. As Wikipedia puts it:
Engineering
When a physical object maintains the same density and is scaled up, its mass is increased by the cube of the multiplier while its surface area only increases by the square of said multiplier.
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.
But, you see, that is exactly the problem. Many of these observations are based on skeletons AS THEY WERE FOUND... far larger than modern equivalents that are at the extreme edge of functionality... but without the stress modifications that would be expected with the doubling or trebling of size. Its like scaling up a mouse to the size of an elephant and still having it look and work exactly like a mouse.
The scaled up beasties are larger and apparently more massive without the compensating adjustments of the structural members that should be required to handle their larger weight and muscle requirements. That's why I mentioned the unadjusted and uncompensated breastbone keel of the Teratorns, the bone to which the flight muscles connect...flight muscles that would have to be huge to allow a 500-600 pound bird to fly... and the wings are also not compensorally larger to provide the added lift required to carry a bird that large - while it is only 3 times larger than its modern cousin is 27 times more volumetric and 27 times heavier. Again referring to the Wikipedia article on square cube law:
BiomechanicsThere is no evidence what-so-ever that the density is any different between modern animals and extinct animals.
If an animal were scaled up by a considerable amount, its muscular strength would be severely reduced since the cross section of its muscles would increase by the square of the scaling factor while their mass would increase by the cube of the scaling factor. As a result of this, cardiovascular functions would be severely limited. In the case of flying animals, their wing loading would be increased if they were scaled up, and they would therefore have to fly faster to gain the same amount of lift. This would be difficult considering that muscular strength was reduced.
That is, of course, the central theme of my post. We don't find skeletons. we find fossils, and in the case of mega-dinos, we find a few bits and pieces.
Much of the compensation for the weight problem would be found in the internal structure of bones. Are they bird-like?
Again, you assume that because bio-physics is not a mature science, the uncertainties require overturning Newton and Einstein. I say bullshit.