A seatbelt or airbag is a safety device that is there as a last resort, sensible people will drive according to their own limits of skill (rather like sailors), and have various other safety devices that will reduce the chance of having an accident (good brakes / abs), and if an accident should happen, if the speed is not excessive, the collapsable safety zone will give a good degree of protection. However, as you have pointed out there are some occasions when the crash is beyond your control, and that is where the seat belt and air bag will help as last resort. Much like a life raft.
I agree the number of fatal car accidents is much larger than the number of drownings, however the number of car miles is also vastly greater than the number of sea miles sailed. But it would be false to conclude that someone that only drives a small number of miles annually does not need a seat belt, a seatbelt, like a liferaft is there as a safety device of last resort when something unexpected happens.
With respect to the force 7 and foundering, I have been on more than one occasion in an unforecast force 7, had I struck say a sub merged container, or an internal plumbing fitting had sheered letting in sea water, or water ingress caused a short that sparked a fire ( I could go on), I would have had to look at plan B or C.
Having listened to the VHF traffic during that time, the emergency services were dealing with quite a lot, and in one case the boat had a weak battery but luckily another boat relayed their VHF calls. Given the amount of emergency calls they had on both occasions, it was clear that resources would have been stretched to cover every call. From that I surmise that sometime I cannot rely on the emegency services to get to me on time, I may need to have an alternative (i.e. a LR)
So yes my plan is that the life raft is a complete waste of money, and I would only contemplate getting in one as the boat went down underneath me.
By definition, you will not have anyone on this forum that needed one but did not have one !