I believe we are way off base in the U.S. at least with how we train junior tennis players. The basketball model that someone mentioned is on cue. I played Div. I basketball (and started tennis when I was 5 yrs. old; dad played in the NBA) and if you look junior basketball development, we play a lot of pickup basketball and that's why so many kids come from the inner city. These are essentially simulated games.
The point Coach Nott is making is there's no substitution for actual points and sets. You can toss balls all you want and drill all you want but nothing mimics actual tournament play, like a practice match. Additionally, if you are a competitor, even in a practice match, you'll deal with some pressure (not the same level as a real tournament) but nevertheless it's good to deal with.
The real issue is parents and coach who won't let their kids play practice matches, and furthermore, if they do, they sit against the fence and watch their every movement. This is so damaging b/c it teaches the kid to rely on the parent who, by the way, can't help them on the court, but importantly, it doesn't provide an environment where the kid feels comfortable enough to try new stuff and add to their games.
During pickup basketball, that's when we expanded our game and added new dimensions, moves and shots.
With that said, a great coach is a necessity as tennis is about fundamentals and technique. You can go quite far with just a great coach, practice matches and tournament play but, of course, that approach is damaging financially to the private clubs and academies. The only caveat is if you are in a poor section, it may be difficult to find adequate practice matches as you can only go so far playing the same 5-10 folks over and over . . . you need variety of type styles to play.
Coach Nott was referring to practice matches (not 500 sets of tournament play for a junior but a combination of both).