At the risk of self-promotion, balancing sample size and recency is exactly what my projection system (DARKO) is designed to do. You can see Jaylen's current talent estimates in any stat, and his overall progression as both a three point shooter and free throw shooter. These estimates account for the amount of noise in any given metric, so are more skeptical of shooting talent changes, and more credulous of other stuff (e.g., shot selection).Its worth noting that, while I believe Jaylen Brown's leap is real and sustainable, we are still operating with a relatively small sample size.
There's also a chart of his progression in a box-score only metric (similar to BPM). Ingram and Simmons for comparison:
Truly a remarkable improvement.