I think there are a lot out there like this unfortunately. We started our run in nationals when our player was dominating (ranked 1) in our section at age 12. After a few, he won a level 3. Went deep in some L2s then won those. Eventually won a level 1 in singles and doubles. At the L2 point we simultaneously moved into ITFs, same process, won the G4 and G5s and then worked up the ITF ladder. This was over years, not months. Yes, there was a disastrous L1 where he went out first round, it happens, they are just little people btw. But we didn't waste much money ever going to events he shouldn't be at. Every win or loss is about building experience and confidence - which become the most important factors once the physical tools are in the shed as they say. Getting blown out however, is not the experience you want over and over. If you aren't dominating your section, then nationals are not a good use of time and money, unless it is a fun vacation break as well. Taking all those steps builds experience (and confidence) all along the way. When in finals, we knew pressure was never an issue because he had been in them many times, all the way back to the lower level sectional events he started with when he was young. Carries into college or pros. Using the building blocks as you described (neighborhood - locally- sectionally-nationally-internationally) makes them really strong when (and if) they reach the top.
Learning to play and win versus someone younger, older, better, weaker, when family is there, when college coaches watch, when scouts watch, when the cute girl watches, when your strings aren't just right, when it's windy, when you have a cold, when it's a final - and many other variables - comes from working through the process. "Betterness" doesn't ruboff just from attending, it is earned through a very long process. Skipping steps catches up with a player at critical times. You can see it in a match. The "I've been here before and you haven't" strength/resolve brings a lot into a match for that player.
