in the NBA not enough time to let new players mesh with each other? That seems unlikely to me. Maybe for the NBA your theory hasn't been tested recently, due to the usual length of contracts.

From the NCAA angle, we also don't have a huge sample size of entirely rebuilding teams with good players from the portal. Back when transfers were restricted, NCAA rosters also usually weren't totally revamped in a single year.

So it might work for Louisville or Kentucky if they bring in a lot of veterans - a lot of 4th or 5th year players who are often more mature than 18 year old freshmen.