You may be right, but:
Per his NFL draft profile:
"Smith is the rare commodity who is truly hybrid in the sense that he has the athleticism, speed and physical makeup to play any linebacker spot in either the 3-4 or the 4-3. But he was somewhat miscast at middle linebacker at Notre Dame"
He is a bit small for MIKE in the NFL, but once he gets his knee straight (assuming he can), I think he'll put on a few pounds and be okay, weight-wise.
The 4-3 defense was created by Landry to keep the big guys off of the MLB so he's free to make plays, Smith (again if he recovers) has the speed and movement ability that you need in a MIKE. Lee was great at MIKE, and he isn't the biggest guy either, was listed at 236 lbs in his NFL profile.
And the draft profiles are wrong often, as a matter of fact Lee's said "Does not have the smoothest hips and struggles to maintain speed in transitions. Lacks burst to stick in man coverage and limited top-end speed prevents him from being a sideline-to-sideline player."
But he's great sideline to sideline, so I think Smith can be good at MIKE, but it all depends on his physical recovery.
We'll see...