for starters this is especially really rare. Most late round picks who make it tend to be either relievers or unathletic corner hitters who hit in college but don't project as mlb athletes and just never stop hitting in the minors (like tyler white).
That a 30th round pick makes it as a starter is really rare.
I think those are really accurate points you are making. Tyler White is a great example. Dude...just...kept...hitting. He is also a good example of a player who isn't at a Baseball powerhouse in college but still gets seen. Western Carolina is a really great program but isn't exactly the first team someone thinks of when they are discussing big time college Baseball. But they are D1 and usually schedule a few ACC & SEC opponents every season. If you can play the scouts will find you.
Yes, but to be fair there are tons of guys who hit 300 with power in small schools and are either not drafted or they are drafted and hit .200 with one homer and 30% Ks in rookie ball and then just disappear from baseball.
Athleticism and tools do matter and most undertooled performers do stop hitting at some point when the pitching gets better. Guys like white are really an exception and teams were not super high on him either, they just took a flier on him and said "May be he can continue, better get him in the late round than a coaches son who is just a roster filler".
But it does happen and the late rounds are there to take a flier on either undertooled guys who can hit or tools guys who can't play but might learn it. Most of those never pan out though.