I haven't tried any of these before, it is just my speculation:
If the PCB is mounted to the plastic case and the metal plate is sort of floating / mainly stabilized by the switches, and if the switches are all connected only through receptacles to the PCB, then I assume the feel of key press will not be as solid as when the switches are soldered in, or when the plate is mounted ("top-mounted").
Haha, I don't think you understand just how solidly the switches are held in! They don't just slip in like they're free-floating, but are held pretty snug, that combined with the plate makes them very solid. In my experience, and I've got five of these hotswap builds now, there's no difference in terms of key press at all between soldered and holtite socketed.
It's true that you can potentially pull out a switch during a key cap pull if the cap is particularly tight, but the benefits outweigh the minor convenience imo. Feel-wise, they're pretty much identical.
I'm a little confused about the idea of the switches feeling less solid in a "tray mounted" setup though. Are you saying because the plate isn't supported by screws? The switches support the plate just as well as if they were soldered, in my experience.