Well, yes, you're being pessimistic, but we've seen a similar situation before, so you're not a nut.
So, if I'm being an optimist, I would say this is a big positive for both Sharpe and the 2022-23 team. He comes in, gets acclimated to college life, gets to know the coaching staff, improves his game practicing with this year's team, maybe even gets to see and understand what road games in the SEC look like, and becomes an even better player for next year's team. But you've mentioned the downside to the deal, which is that he could decide to bolt for the NBA before he ever puts a UK jersey on.
I will say, I think the NIL rules may help a situation like this. I'm not sure what Sharpe's financial situation is like or what his family's situation is, but being able to make money for himself could keep him here longer. (and yes, I know it's chump change compared to what he could make in the NBA) That could keep players who come from humble means around a bit longer.