I struggle a little bit with the macro lens for this type of situation, because in a single at bat so much that may or may not repeat itself in the long term can manifest. It's also prone to us seeing what we want or hope to see, we want Busch to be a success so him having an 'almost' moment burns brighter in our memories than the inning before when Seiya missed a backup slider that he could have sent to the moon with 1st/3rd & 2 out. You could write an article with very similar tenor about that moment, and about the differences in being a strong hitter v. making the leap to be an elite bat, etc.
That said, my unscientific opinion after watching Busch for the weekend is that I'm reminded a lot of Happ. Both are very patient, let the ball travel and will try to use all fields, and they're of similar stature and from the same side of the plate. That'd be a very nice outcome because even with the higher bar at 1B, a 115-120 wRC+ from Busch would play very nicely in deepening the lineup to consistently be 6+ hitters of strong quality. But what makes Ian Happ work well is excellent pitch recognition, and watching Busch's at bats against Gray I don't think he was picking up his repertoire very well(swinging through a 2 strike fastball, and not tracking the slider particularly closely). Contrast that with Happ seeing the ball well enough that he went 2/3 w/ a 2B off Gray, and that's the small sample comparison I'd make about Busch's ability to make the jump at the MLB level.