PG, I just don't understand your long-time contention that a rookie MLB can't have the smarts to play the position.
These days, the pro game is chock full of coaches that make a gazillion decisions and issue orders during a game. Players aren't on an island. Unfortunately there are many (most) Offensive coordinators that lift their leg on a decent run game and decide that passing is the way to go, d*mn the consequences.
And defensive coordinators that chronically ignore what's worked most of the game, then panic and play prevent in the waning moments, result often being the opponent marching downfield with short gains to kick a winning FG. See NE's SB wins.
Collegian LBs have played the game for some time...they do recognize things. They have instincts. And there is help..vets on the DL, other LB's, DBs. The rookie MLB isn't out there by his lonesome. No doubt experience helps, knowing a tram's tendencies, their players over time.
But the offense owns the snap. Even the most astute defensive playcaller is in trouble when an offense shifts things about 5 seconds or so before the snap. And if he starts shouting out changes then, good luck.
If my rookie MLB shows better athletic skills than whatever else I have at that position, I'm going to work hard to get him in the starting lineup.