Since there's no data, I agree it's debatable. I just don't think the likely consequence of a rule change upward, particularly to a three or four-year minimum, would result in more mature and fundamentally sound players in the college game. I'm less sure about the impacts of a two-year minimum but here's my rationale for a three-year minimum:
At least for a three-year minimum, I think many athletes who would otherwise declare to the NBA draft after only one year under the current regime would go to the D-League and abroad instead of the NCAA to get paid. These players have typically made up a plurality of modern NBA draft classes. At this level, I think this would negatively impact the college game.
As for the athletes who would have otherwise declared after only two years under the current regime, I think the consequences would largely be a wash. Some athletes with a high level of raw athleticism (just short of otherwise declaring after their first year) would choose the D-League/abroad, making the college game worse than it is under the current regime. Others would instead stay longer than they otherwise would have under the current regime, making the college game better. I think if the change were instead a four-year minimum, the impact would lean towards being worse at this level because you would have even more flight to the D-League and abroad.
As for the athletes who would have declared after their third or fourth years under the current regime, there's obviously no change.