Earlier quoted context omitted.
If your only had a piano, instead of a computer, your story wouldn't be particularly convincing. People who grew up with a computer, before most other people had one, were lucky to find a rapidly growing industry. Most other people are getting very little for their single focus.
If I only had a piano to entertain myself I probably would not be a professional piano player, you are correct. But that's not the point of the anecdote. Replace my computer with anything else, and the frustrations will still be the same. The boredom and experimentation and learning and moments of clarity and joy and pain will still be the same. Whether I carry the piano into my adult life doesn't matter. I've still…
You can be the most dedicated piano player, but if you later decides to channel that dedication into e.g. writing you are very likely to be struggling anyways. So now you are essentially in the same boat as everyone else.
Young people are mainly struggling because education, housing and long term careers are competitive and costly. Of course dedication can help with being successful in almost any sense of the word. But overall it is very likely overshadowed by other factors as e.g. your position in the housing market.
How many people who could afford a mortgage in a major city in their early twenties, by any means, are struggling with their lives today? Certainly a few, but surely a lot less than those who don't yet have a stable home in their thirties.