A PF to me is to me a big strong player, that can power his way to the net to score. Ds slash him, cross check him and try to knock him down but can’t.
A prime example of this would be Mats Sundin when he was playing for the Leafs. His 6’5 frame and having filled in his body he was an immovable force.
Iginla did a lot of that and he was 6’1. Leonard is a hair under 6’0, he possibly will grow some more. The height between Iginla and Leonard would then be negligible. You make the argument he could be on the lowest side of the PF size spectrum.
The second side of the PF definition is physical. Leonard is physical in that he looks for body check. He doesn’t power to the net. Offensively, he’s a shooter. His game is simple he gets to the slot (usually an opening in the upper slot) and waits for a shooting opportunity. Either he gets fed by Smith or Perreault or he tries to pick some errant pucks or rebounds in the area. Then he does his shtick, which consists entirely in wiring the puck on net. The puck stays half a second on his stick and is off. He has a very good heavy shot. However, he doesn’t do power moves to the net like PF . And in fact he often gets knocked down by players in the slot area, which is very unlike power forwards.