It depends on what Mannix means by probably most valuable, and having listened to the audio it is not clear.
If he means which Celtics player other teams would like to have, then yes, it's Crowder. He could fit most rosters bcs he is versatile and can play different positions.
If, however, we are talking about which player's absence would hurt most the team, I'd go with IT, altho this is clearly very close. Without Crowder we are in trouble, but part of the reason is that we are very thin at the 3.
Without IT, we'd be in similar if not greater trouble, although we have other ball-handlers. 21.9 pts and 6.6 assists per game cannot be replaced no matter who takes his mins.
IT might not be as popular with the scouts as Crowder: he can only play the PG and many teams are covered on this spot. But he still is the player that makes our offence work (and his D too has improved this season).