Plenty of pros an cons for a Rib, some more subjective than others. But there is an important aspect to buoyance and that is stability. It's correct that most hardboats(I guess all modern designs) floats filled with water but i think none of them maintains a reasonable stability in that condition.
I would not worry too much if stuffing badly my SR, pretty sure to be OK if /when empty it with the elephant trunks. I don't know any hard boat of similar size i would not worry in... they typically have the buoyancy much lower so the boat rather turn it selves upside down than keeping it stable as a RIB. This makes a big difference a day things goes wrong.
fun on a boat is inversely proportional to size...sort of anyway