I am not sure whether I agree with the "Compton limit." A particle can be spatially localized as much as you want if you include high velocities in its wave fun

I am not sure whether I agree with the "Compton limit." A particle can be spatially localized as much as you want if you include high velocities in its wave function, and that can happen in tight bound states as well as in high energy processes. To offer an example of the former, the radius of the s1 atomic orbital shrinks as the nuclear charge increases, and if there is a limit on nuclear charge it is determined by processes unrelated to the electron itself. For the latter, the total energies of all particles eventually start acting like photons w.r.t velocity as their rest mass is overwhelmed, and the gravitation or inertia of a beam of light is impossible to rationalize as mass or put on that chart.