Cretaceous oxygen levels were at times comparable to those today, and possibly lower. In any case dinosaurs probably had very efficient lungs, as birds do. Unfortunately there's no way to get DNA that old.
From bioenergetics, fluid mechanics and aerodynamics, we show that if the
atmospheric pressure was higher at the time of the dinosaurs than it is today, we would be able to resolve a number of anomalies which puzzle scientists today. These concern how a giant pterosaur (quetzalcoatlus, with a 12-15 m wingspan) had enough power to fly; also, how a giant dinosaur (apatosaur, with a 12.5 m long neck) was able to pump blood
up to its brain.
Double or triple atmospheric pressure would have lowered evaporation to such an extent that it would have had many other geological and botanical effects that are not seen.
Rather surprisingly, I just found that different oxygen fractions do cause different atmospheric pressures, by altering the density of air, but it's a 15% to 25% difference, not 200%. Maybe it's possible to use this to resolve tensions in estimates of how much oxygen there was. See https://www.science.org/doi/10.1126/science.1260670
There are buffalo on Catalina Island. About 15 head were brought there to film a movie and they've multiplied.
Like a lot of island species, they are smaller than their continental counterparts and when relocated to the continent, they gain on average about 100 pounds and grow thicker fur.
Humans who live at altitude for any length of time can see their lung capacity increase. Human sub populations that have lived at altitude for generations also have other adaptations, such as thicker blood, more small blood vessels, etc.
That's in the current world for just a couple of species.
As far as I understand reality, dinosaur physiology is not adapted or suitable to current conditions on planet earth, including but probably not limited to the way their lungs work and differences in atmosphere.
It literally cannot be answered with certainty, barring some passing ancient aliens giving us the DNA sequences they took last time they were in the neighbourhood. But as a matter of speculation, dinosaurs seem like they were pretty adaptable. Penguins can live in the Miami Seaquarium – I don't see why a dromaeosaurid would do so much worse.
