Yea for sure, a smaller skater should be somewhat more susceptible to big hits from large players.
But for gameplay balance, you should have some kind of tool in your bag to have some resistance to a hit. And like I said, EA does have some logic built into the reverse hit mechanic where, based on the interacting players' height, weight, attributes etc - sometimes reversing a hit can just result in two players colliding and falling to the ice. Kind of like a 'null' of the hit and the reverse hit at the same time.
Your point is a valid one though. I still think smaller players should have the ability to at least 'null' a hit as described above. I would concede that a small player using a reverse hit to absolutely lay out a bigger player is unrealistic though.