Let's not pigeonhole outside WR and Slot with him. He's obviously going to fill the DJax/THill role in the offense. Sometimes, in the bunch, he will be behind the LOS to ensure a clean release (technically slot). If they are playing zone (what teams do the counter the 11 personnel ZBS) he can be outside like Cooks.
As for his size, basketball has plenty of smaller players that were effective (Spud Webb, Allen Iverson) in their roles because of their quickness and agility. McVay will ensure he plays in space. Can he get injured? Sure thing. Everyone can in football. Heck, AD is "too small" to be a DT, right?
Look, I don't know if he can learn the nuances of this offense. I don't know if he can learn how to beat press with moves like DJax does. But I worry more about those things than I do his size. The focus on his size and weight seems to me the misdirection that Sean encountered when he was hired as a "too young and inexperienced " head coach. Let's just see what happens, my friends.