I disagree. I see a lot of baseball at all levels, and while each tier shades into those above and below, the overall progression is clear. The player pool is relentlessly whittled as you go up the ladder (the whole system is really dependent on an enormous reservoir of unrealistic optimism among young players, and their resulting willingness to work very hard for little money).
Many players never reach the majors because they hit unmistakable walls in their development somewhere along the way. A guy may look great in rookie ball, very good in short-season and low-A, and then he crashes in high-A. He may get busted back for half a season, look good again, and then promptly crash again on re-promotion. When pitchers start to command their secondary pitches (and that’s about where that happens), that’s the end of the line for more than few hitters.
I do think that the size of the particular step between AAA and MLB is often exaggerated.
Major leaguers on rehab stints are not exactly playing to their top form, but they do hit .500 or throw short-outing shutouts often enough that they’re clearly a little different than their competition at that level. And it’s very rare for a college team (playing hard, with something to prove!) to actually beat a quasi-major team just getting in gear in the spring. A few years back when the Tigers were really bad they tied a college team in the spring, and that was seen as an embarrassment.
Of course anything can happen in one game here or there.
Well, yes, because passable major league players themselves regularly go not-much-for-the-series at the plate, and it’s easy enough to look passable in the field, especially the outfield, for just a series. Your college player may not stick out to a casual observer as not belonging on that team, but he’s not likely to look better than mediocre either.
In a way the differences are all small things, but there are a lot of small refinements that players make as they climb that ladder. The Crash quote is accurate, of course, but it doesn’t acknowledge how hard it can be to make up each additional tiny increment of improvement against ever-tougher competition. The most telling single fact is how rare it is for players to succeed in the major leagues without time at every or nearly every level working up. It happens for an occasional phenom, but rarely enough that the whole structure is clearly necessary to develop typical modern-MLB-quality players.