Sounds like some great diving. I'll try to be impartial
If It were me in the situation you describe, I think it would come down to comparing the worth of the following general styles of DPV that might work for you. Im sure you do some additional diving to that you describe, so this may further influence you.
A) A larger scooter I never had to open during the day, but most likely couldn't travel with.
B) A smaller scooter that I may have to swap batteries (probably once) during the day.
For some people its black and white. If your always out on a RIB in the cold and wet, opening a scooter to change batteries is a huge NO NO. Some people travel a lot, or live somewhere that shipping large lithium and dealing with all the hazmat issues is not possible, So having a scooter that was travel friendly is mandatory.
Sales hat back on:
Sounds like a P1 will easily get you 2 dives with massive improvements over the Sierra, but probably not 3 dives. So I would need to swap batteries after the second dive. But if your OK with the modular Piranha infrastructure, its low risk as you can always add a battery module to create a P2 at a later date and then you would never have to open the scooter.
Be a little careful comparing spec sheet numbers. They are not always true for some manufactures. The original Tahoe group are pretty solid, SS, Logic etc, I don't have much data on Bonex other than the Aqua prop I own.
Generally when testing scooters I've found quoted run times are correct, but max thrusts are overstated. Its also generally reliable to compare lithium battery capacity. A 500Wh scooter will generaly run for 2x the time of a 250Wh scooter.