I'm not convinced there is much correlation between swimming and scuba diving other than knowing how to properly swim. Most of the emergencies that I can think of that would arise from scuba diving that resulted in your being on the surface would require your being able to stay focused and possibly able to tread water for long periods of time, especially if for some reason your equipment was lost.
If your BC is holed and you have no buoyancy available in your kit, DITCH IT.
Guess what - if you have a wetsuit on, you're positive. MAJORLY positive. Like 10 lbs or so if you have a 3mil, and even more with a heavier one.
You ain't sinking even if you try under those conditions. Tread water? Why? Float on your back and enjoy the ride.
If your BC is still working (even if manually), put some gas in it and play "raft". Again, lay back and enjoy the ride.
Yeah, there are issues with being lost out there. Like dehydration, exposure, even sharks. But not floating - unless you're just plain stupid and keep your weight belt and the negative parts of your kit on - and if you're lost at sea, why would you?
Comfort in the water and a reasonable level of fitness is important to diving. Swimming, per-se, is not.