The best way to do physics is to experiment. You never know, and you always have to make sure that nature agrees with you. Otherwise, you may as well write fantasies, not even science fictions. After all, the novels you sell will contribute more to humanity than your untestable physics. Test is everything. So, we’ve got electrons, protons and all sorts of charged particles accelerated to near the speed of light with particle colliders. So far, everything agrees with special relativity perfectly, well, nearly, as experimental errors always exist. However, the errors have been small enough following decades of experiments that we now believe that special relativity is true and beyond doubt. So, everything scales, even at the quantum level. Non-elementary particles maintain their stability perfectly even near the speed of light. They don’t break apart before they hit and perfect scalability is the assumption in all calculations we carry out in particle physics. All chemical reactions, presumably, will remain the same within the local frame of reference regardless of its speed. Perfect scalability! That’s the problem.
So, space-time continuum is not a concept. It’s real. Otherwise, we must prove that quantum gravity can maintain the apparent continuity of space-time for all known quantum mechanics, which is a tall order. Yes, gravitons must be that small if they do exist. Otherwise, they exist outside of the observable space-time continuum to which we have access, in which case we need to access higher dimensions to test quantum gravity properly, assuming it’s indeed quantized at the microscopic level. Why can’t continuity simply exist physically? Is it so difficult to simply believe that mathematical perfection simply exists in nature? Well, it’s not a problem at all. It’s just that as soon as you believe in continuity, you stop doing physics. After all, I can believe that the surface of the ocean carrying boats is perfectly continuous and stop there, too. There will be no science or whatsoever as soon as we decide to simply believe. But, what if space-time is truly continuous? Aren’t we wasting our time here, not to mention the dedication of so many top minds in the world? Well, this is why so little funding is given to this type of research. This way, those top minds know to find their jobs in other supposedly more useful fields. Physicists are no longer as respected as before, but there are still plenty of people living in the past glory of physics. For them, physics is the meaning of life. You ought to appreciate their stubbornness, because they make sure that your nation is ahead of everyone else in the physical understanding of this universe, much of which is applied in military technologies. National security is not a joke.
You can be one of the stubborn in taking the proactive approach to quantum gravity, namely, to churn out as many plausible and testable theories as possible, or you can take a more passive approach by working on quantum gravity in your spare time and using interesting physical relations only. A good starting point is to figure out how the Higgs field works under the relativistic framework, where everything is so ever scalable. It must be that length contraction compresses the Higgs field so it works more like a density function within space-time continuum, hence the separation of inertial mass and gravitational mass, right? How intuitive!