Indeed I would agree that boats with both
deck and
keel stepped masts should be considered. I have a
ketch which has both.
I am no rigger by profession, but from my understanding the shrouds should be what holds the mast up (and is tuned to have it in the right place) for most boats (excluding unstayed / freestanding mast rigs - like many with a wishbone boom).
Where the mast is stepped has more to do with where the forces come down. The
keel is a good strong place and does not require the superstructure to support the mast. On the other hand with a
deck stepped mast one can perhaps prevent leakage a bit more easily and have a less bulky item or sometimes nothing taking up living or other space (more flexible for different layouts and esthetic design).
In other words, unless you are designing a
boat, I would just get what you like as a total package (and not worry about where the mast is stepped).
Also, regarding
blue water cruiser and self righting, I think the biggest distinction is cruiser vs
racer. A
racer will (in general) have less beam and have a relatively overpowered sail plan to get more speed (especially with little wind) over stability. Note it is a focus on where to compromise - racers are still designed to be stable, just in comparison one has to watch the numbers more closely and consider to reef earlier (whereas with a cruiser you may be able to get away with more in general).