...and that is not considering that most divers also carry a SMB of some sort (my 3 footer is 10lbs lift and 6 footer, 20 lbs lift) with some of us also carrying a lift bag depending on the dive profile, that can all be, as a minimum, inflated either orally or with a reg.
1. BCD is used as primary buoyancy.
2. Drysuit is redundant buoyancy.
3. BCD oral inflation is the third redundancy option.
That's quite a lot of options at your disposal. Do you really* need a fourth?
*question assumes proper training and usage of equipment, proper weighting, balanced rig and application of safe diving practices.