Things we can agree on: Booker isn't a good player comp for Primo, Primo isn't too likely to turn into a Booker-like player.
I disagree with most of the rest, but it's mostly opinion one way or another, so it's a pointless discussion to have until Primo has more games, experience, and reps at the NBA level and we get a clearer picture of what he is and isn't. Again, even Booker wasn't "Booker" coming into the league (and his terrible teams' situations at the start of his career allowed him far more protagonism, shots per game, and reps, than Primo has gotten and probably will get next season, too, even if the Spurs tank out a second season), it's far too early to put a ceiling on Primo's projected career.
I also find hilarious that you think all of Booker's athleticism, scoring at the rim, etc, makes for only a 3ppg difference regarding what Primo could do... If Primo's a 18-21PPG scorer someday, it means he's already found ways to leverage his athleticism and shooting to great lengths, tbh. An odd cutout you make there. More PPG or less is, again, in most cases, a direct result of team composition and talent level (same way Dejounte's PPG saw a noticeable, and predictable, jump this season, with DeRozan et al off the team) beyond simple talent level. I don't see anything in Primo's game so far that marks a "death knell" to his ceiling that he can't possibly get over; he can improve his first step, his handles, he could tap into a post game (especially if he continues to play as a big guard and continues to grow, he could go the Luka route and bully smaller players). Lots of things he could do with proper development.
It's fine if you want to rule him out. I don't. You sound like the people saying James Harden had a 6MOTY ceiling back in his first couple seasons, and exactly for the same motives: lack of an explosive first step and otherwordly acceleration (little did we know it was his deceleration that would matter most), etc etc.
Let the kid play a while before putting ceilings over his head is all I'm saying, bottomline, tbh.