I don't think he's making the claim that Bateman is 100% a finished product and there's zero chance he can improve or stay the same to be a viable MLB player. I'm sure the Blue Jays view every prospect they acquire as the possibility to unlock a guy to perform at their best possible level. Statistically though, it's way more likely that Bateman is who he is, and he's not making some Jose Bautista esque journeyman to HOF transition. Not to mention, once again, there's things in his profile that prevent him from making changes like that, or if those changes would even result in improved performance.
It's entirely possible Bateman has found his relative lack of success to this point by being the type of hitter that he currently is: patient, contact first approach, not putting the ball in the air too often where he doesn't have the strength to make it do damage, and putting most of his energy into being a good defender and runner. Maybe you tell him to change his swing or approach and now he's 2026 Myles Straw with an improved barrel rate and ISO, but getting on base far less and a lot of his batted balls in the air going for easy outs. Who knows if he even has the talent to make such changes. Hell, Vladimir Guerrero Jr. with all the hitting talent in the world can't turn around from a season long slump. What makes you think Brett Bateman and his 2nd percentile Max EV, 15th percentile 90% EV in AAA, can even do this?