The purpose of hitting the water and giving the “okay” signal is to let the boat know you haven’t become a lawn dart. With an empty BC and dry suit, you had better be negative or you are in for a short dive. Depending on the type of tank(s), you can a swing 5 to 8 lbs. The amount of air in your drysuit is going to determine your thermal protection. Finishing a dive with a suit suit squeeze to stay on the bottom is just as miserable as having to kick to stay down. Being 10 lbs negative at the start of the dive is not unreasonable and with no air, you’ll tire pretty quick. Once you hit the water you will become more negative the deeper you go. Suit squeeze will limit your mobility, too.
People have died like that. In one of the books about diving the Andrea Doria, they described a dive doing just that.