I wouldn't call a maneless lionhead a pure lionhead, and you would never, imo, see a maneless lionhead coming from a reputable breeder. And I wouldn't call any rabbits brachycephalic either, at least not in the same way its used in other species. They don't have a stop in their face, like dogs or cats do - their eyes are on the side of their head, so a shorter face doesn't fold or constrict the breathing passage (and besides - most the "short faced" rabbits get that effect mostly from having thick hair on their face that stands up vertically, not from the actual shape of the skull. Unfortunately a lot of the dwarf breeds like netherlands and holland lops are prone to issues anyways, but that is more due to the number of unethical backyard breeders those breeds attract - quality lines from a reputable breeder shouldn't have any teeth or eye issues.)
Lionheads should have a bold head with good width and a slight roundness between the eyes, but should not be round in all directions. Their heads are less round than, say, netherland dwarfs or holland lops. The lionheads that you would be seeing with the long narrow faces are most likely not pure lionheads. Lionheads don't call for a round face but they fault severely for a long, narrow face. Most show rabbits have, on average, shorter, wider faces than the average pet stock rabbit
