Why do you not like looking more deeply into how gravity works at the quantum level?
What is the good reason, you allude to, why you think there is no viable quantum gravity?
Good questions, firstly I think relatively is complete it is how nature is, if it is the correct 'nature of nature', then it does not need to be replaced, at best you could do a quantum mechanics interpretation of relativity, but that is just playing semantics with math.
Plus quantum mechanics does not really deal with space and time, and it cannot explain why c is constant, or why time and space length are not constant. Quantum mechanics it more about matter.
Quantum mechanics is not really a theory in the traditional sense either, and very little progress in happening in the what is mostly a theoretical field. Quantum mechanics yields very little (almost zero) new insight or understanding of how nature works
Not a huge fan of quantum mechanics!
As for 'the quantum level' know about how anything works at 'the quantum level' in reality, and it's not even close, 1x1020 Planck lengths exist in the size of what we think is the size of an electron, and we are only guessing that size (about the wavelength of a Gamma ray as well).
So we can do nothing at the quantum scale except guess, we cannot get any useful information from the real world of the quantum scale world, so you can say anything you like (and they do).
I don't think quantum mechanics is the theory of everything. (I don't even think it is a theory of anything!).
For me, what is more interesting is what is it about energy that when it is in the form of matter with mass that gives space that length (or curve) property? But even then, there is much speculation and assumptions. The standard particle model does a good job, but it is only a speculation, we can never know how the machine actually works by smashing the machine apart and observing what comes out.
I think the reason why matter creates a length of space to exist in, is because matter needs a length of space to exist in, matter cannot exist in the same point in space as other matter, but energy can.
What gravity is, is the length of space (be it stretched or curved), what relativity explains is how matter gives space that length, what we feel as gravity is the gradient of that length, matter wants to be in as low an energy state as possible, the longer the space length the lower the energy (energy distributed over longer space and time). Matter 'falls' towards longer space. (because the same speed is faster in longer space, if the meter is longer then 1 meter per second is faster that 1 meter per second in shorter space).
TL;DR I don't think a model of quantum gravity is necessary or justifiable. (or even possible).