Quality of play has gone up because the evaluation process is more efficient. That's the reason we have the one-and-done rule-- to help evaluators.
It's hard to accurately pick high school players. It's easier when you have a year of college evaluation. The more efficient the evaluation process, the less busts you have on the floor. Early 2000s basketball was littered overmatched high school players fumbling around the court. They had to play early because they were picked too high.
Now, the draft is better, the skill level is better and the league is better. The rule worked.
I don't really care about fairness. It's unfair that LeBron James was born with his genes. For every high school player who gets into the league early, a fringe player is pushed out. It's a zero sum game.
All I care about is the talent level. The one-and-done rule has greatly improved the talent level, which was the point.