I actually prefer the ultralight (read flimsy if you want) keys.
Just easier on my aging wrists and fingers.
I liked the light action as well...you get very used to it, especially if you aren't coming to it from pianistic style, or just after using a weighted keybed.
Most of the synths and keyboards/organs I played, except my old Polymoog (which had semi-weighted keys), had a lightweight touch, and it works for most of the sounds, probably with the exception of acoustic piano, but, again, it's not hard for an experienced player to adjust.
The velocity sensitivity is pretty good on today's lightweight actions (I can speak for PSR)...generally you can press a key slow enough so that there is no sound, much like an acoustic piano, so the
range is there...just needs to be approached differently.
Ian