The caveat here is that we generally DO have a feel for whether a contract is an asset, even mildly, at the time it’s signed. By that standard, since Jaylen would likely bring back minor assets if he were traded tomorrow on this deal, it’s a good contract.
I agree that we don’t know the more important thing: how the Celtics evaluate his upside/work ethic. We do, however, know that they tend to evaluate NBA players well, and also have been reluctant to pay up on extensions. Those factors indicate that Danny et al think very highly of Brown, and there’s a decent chance they’re right.
It’s good to be realistic about the limits of our knowledge, but it’s just as important to catalogue what we can know/infer (with error bars of course).