2017 infiniti Q50 AWD
I had a 17 premium AWD with RSR down springs same as OP and it rode in normal circumstances practically stock. I do not experience any of the things OP mentioned.Sounds like your stock shocks may be blown from the lowering springs.
You really should be sharing this kind of info in your initial post before posting a strong opinion.
I actually suspect that your dampers are blown or failed and probably need to be replaced. Lowering springs can impact the life of stock dampers, but I also wonder what happened to the vehicle that could've damaged the suspension before the rebuilt title. Maybe the "rebuilt" didn't address the suspension.
I suspect you are correct, the "rebuilt" could be contributing or possibly whoever installed the springs spun the strut blowing it or causing it to leak or something along those lines.
A coilover could be a bandaid fix covering the real issue or fix the issue but only because the issue was the strut not spring. Its slightly lower and slightly stiffer it shouldn't have a dramatic impact to ride quality. Plenty of positive reviews and people commenting the same, enough of them to make me suspect the ones who do have negative reviews actually have other issues or it was install error.