Bear with me -- I'm a science teacher. And I'm not trying to be snarky or anything. I am genuinely trying to answer OP's question.
The reason I keep telling myself "my kid is pretty good... but it doesn't really matter, he's 13" is because I think baseball progress is non-linear. On the graph (I made up) below, each curved line represents one kid's progress as s/he ages.
Just because a kid is better than most at age 14 (highlighted yellow strip in graph below) doesn't mean he will keep getting better every year as he grows older. If he did, he'd probably end up a major leaguer! Based on what I've read here, that happens to a few kids. Most kids hit a plateau or get injured or lose interest or want a social life outside the gym or get cut or decide career preparation is more important than staying on the team (or ...) . Those are all the trajectories that peak and roll over, sometime between 14 and 22. On the other hand, some kids are late bloomers - those are the ones that might be average at age 14, and then take off later in high school.
I don't know how common each type of kid is, though I would guess "above average then plateaus" is pretty common. The area I shaded in blue is the one where I guess most of our kids will end up. Then there are the superstars (Trouty, representing my current South Jersey) who just blow by everyone and stay there. Even those guys have to be lucky as well as good.
So bottom line is.. yes, for my baseball-loving kid's sake, I'd rather he be awesome this year at 13 than be average. However, if he is awesome this year, I will resist the temptation to assume he will also be awesome next year. I will encourage him to focus on the present and do what he can now to get better and help his team. (I will keep reminding myself to do the same!) As long as he works hard, enjoys working hard, and keeps up with his responsibilities, I will keep schlepping him around and paying for his baseball stuff. I will enjoy the ride (and the day-dreaming) as long as he is willing and able to play. I will also keep encouraging him to keep up with non-baseball things; I want him to grow up a whole person and not to feel like his whole worth as a human depends on his baseball performance.
Sorry for long post. I feel like OP is wondering the same things we all are, marveling at how determined and motivated our kids are, and keeping our fingers crossed that they will stay healthy ... and we are all trying to manage as best we can.