What role is Gainey filling that we don't already have on the roster? His numbers reportedly plummeted his sophomore season due to being forced into the lead guard position. So while Assist Rate went up marginally, all other shooting metrics stayed the same or shot down. He doesn't draw fouls either, so he'll fit right in with the rest of the team. He does steal the ball at a good clip and is a pretty good FT shooter, but shoots WAY too many long 2's.
So it doesn't sound like he can be an effective stopgap or backfill for ZZ. He obviously doesn't fill our need for a stretch 4 unless you argue that Mashack can do that and Gainey can slide into where Mashack was. Nothing against this kid, but unless he regains the 3-point shooting from his freshman year, all I see him doing is either not playing very much, or he takes developmental minutes away from Carr.