Based on what, exactly?
Did I miss him having a big game in summer league or preseason?
As far as I'm aware, he's had a couple of games where he hits a few shots, but I have yet to see him look like a "fixture."
Is there any evidence yet he can consistently get open and hit shots against NBA defenders? How about defending NBA scorers?
It's a matter of personal opinion, really, which of course can and should be taken with a grain of salt. My primary arguments are, and do not go beyond, a) He is NBA-ready and can immediately help the team (in a limited capacity), b) He would benefit more from being with the team than in Maine, more often than not, and c) He will be a Celtic beyond his rookie contract.
The rationale is really simple, as I listed observables that appear to be associated with success at the next level: supreme confidence, high BBIQ plays on both ends of the court (crafty assists, help defense), high effort, and ability to move on after making one of many expected mistakes (unlisted, reference to cutting instead of flaring on a semi-break with IT pushing the ball). Re: confidence, I observed several instances of a vet talking to RJ during a time-out or on the court ... a teaching that, one would assume, a vet wouldn't go out of his way to provide if he didn't think RJ was prepared to digest and act upon. His demeanor in these scenarios, and during the Olimpia game in general (his
first professional game), were impressive as well.
I expect we will reach a snafu here because we're discussing two different things -- statistics supporting performance, versus observables supporting capacity. In what little I have seen, he appears to have both the talent to make a significant contribution, and the intelligence/maturity to make good on that talent (perhaps beyond).
Final point: Some players have historically elevated their games when paired and competing with superior talent. I place RJ in that category, as he appears to fit the mold of said players pretty closely -- high BBIQ, focus, confidence, translatable skills, and motivation. If that is the case, he belongs with the team more often than he does in Maine, for his development and the team's benefit. Is this presumptuous? Sure, that and bold by CB standards (that tend to interpret stats and... beyond that... very little). I'm just focused on that "very little," and while the value of that may be in question, and the reality may be that I'm way off-base... I still just feel confident in him with respect to that mentioned above.