Gavin probably slots in at around 11 to 12 PPG, if he plays starter minutes (26 to 28 MPG).
How effective he is or isn't will depend on what players are on the court with him. The more defensive players who can get deflections and steals, might be able to get RU back on track with layups in transition... the lack of footspeed on this past year's roster, will not help Gavin, if it's another slower footed roster around him.
A roster with a Taran Armstrong type guard from the transfer portal, stepping in for Mulcahy, mixed with Simpson and his ability to push the ball, will allow Gavin to roam and find spots to shoot.
Gavin (to me) isn't close to a 1 and done type of talent or has that type of mindset of getting to the fastest path of being a 2nd round or Free Agent on a NBA level. He's more grounded and is interested in winning games at the college level, definitely interested in teaming up with Ace Bailey, Deliquan Warren and hopefully Dylan Harper and Tyler Betsey etc.
The longer Gavin plays at RU, the better RUs program becomes. I don't see a situation where Gavin comes to RU and bypasses getting a degree, so I would guess with a very high level of confidence, he's at RU a minimum of 3 seasons.