I think and most experts agree that boarding from the stern is a
bad idea in all but the most benign conditions. Certainly there
are times in the Med when it's fine, but other times are not ok.
Warm water isn't the only critieria.

A quick exit from cold water is the most important criterion. The
colder, the quicker the exit must be. For most marina and harbour
dunks, stern boarding is safe, and they're the most common events.
As many people have discovered, it's very difficult to board a
hard dinghy from the water.

If your stern ladder extends about 2 ft deep into the water, stern
boarding becomes safe in a much wider range of conditions. And if
it's unsafe, you can always go back to assisted boarding - over
the side, whatever. If there's someone to assist you. And if
there's time before hypothermia sets in.

JimB