This is ridiculous... The responsibility for this is 99% with the diver and 1% with the boat, and that only for allowing the diver to go in the first place.
1 - that the diver's "hat" and mask kept coming off on the entry demonstrates a significant misconfiguration issue that the diver was allowing to persist, apparently (from the tone of the post) because he didn't know to fix it.
2 - the diver shouldn't have been on the surface to be hit anyway. A back entry is a negative bouyancy entry and recovery and normalization should be at around 10'. Staying on the surface, or surfacing after the entry, poses a risk to other divers and to the diver himself.
3 - this has nothing to do with diver size. I am not large and I'm no olympian athlete. I've done back entries in singles, doubles, doubles with stages, sidemount, with and without a scooter. I've gone with divers as short as 5'1" on back entry dives.
4 - there isn't a need for some kind of more formalized, more controlled entry system. A back entry is *not* a difficult diving skill. It's a standard taught, basic, entry level skill. People either know how to do a back entry or they don't. If the OP had done his back entry properly then the accident wouldn't have occurred. We don't need DM's and boat captains standing over and watching every second of the dive -- that would be annoying, demeaning, detract from the dive, and be unproductive since the DM can't watch everybody at once anyway and if they're paying attention to this then they're not watching some other diver get into trouble.
5 - DM's and boats do not "ensure safety." DMs and boats have particular responsibilities, like making sure divers don't get chopped up by the propeller and leading the dive.
6 - unless there are *very* significant waves, someone who is physically fit enough to be diving at all should not need help staying on the edge of the boat, at least in a single tank. It is not physically hard.