I think you are on the right track with focus. Speed kills as they say. I once read that a kid will typically gain 0.3 per year upto age 16. Then it's harder to make gains: like another 0.1 per year upto age 18. So your son will likely naturally be sub 7.
That said, I have a 2023 MIF who is a good fielder but undersized and runs 6.85-7.0. If he was a little faster, maybe it would have made a little difference. We know kids who are 6.5-6.7 and they get a lot of attention just from speed. My 2025 is a portly 6ft, 200lb pitcher and runs 7.0-7.2. But how he does it is he stands back from the laser start around 6-12 inches. Thus he trips it after he is already going a step. I've also used the app "seconds count" to exactly time them on a football field and slow down views of their foot strike, cycling, arm motion. I had them do a lot of A skips, B skips. But really you should have a professional help you.