I'm curious what you're basing the above information on...mostly a hunch? You've said it a couple times, but have you looked at the talent/rankings for the upcoming class of freshmen and their draft stock and then tallied what Kofi would need to bring to the table to be a lottery pick, or have you just focused on the potential financial payoff if that were to happen? There are tons of wing players that are (currently) viewed highly by scouts that will be eligible for the 2021 draft. Meanwhile, you have a NBA team that just recently decided they don't even need a center in the modern NBA to be good (the Rockets). This is why I question the argument that he'll be able to substantially improve his draft stock -- it's already stifled by the position he plays and his lack of perimeter mobility, two things he (probably) won't be able to change. If he can start nailing threes and make teams think he's a beefier Brook Lopez, then perhaps his stock substantially improves. But what if teams think he's Caleb Swanigan and he's right back where he started (minus one year) or even worse due to the strength of next year's draft?
I'm not saying that he should leave this year or that he'll even have much draft stock at the end of the year, just emphasizing the amount of factors that go into a decision like this. It's easy to think that improvement is linear and that improvement is linearly correlated with draft position, but both of those are not necessarily true, particularly when it applies to a true 5.