I had lunch with my coach last Thursday. He was a first round pick, pitcher of course, had a somewhat injury prone MLB career. He was musing back to his start in pro ball, right out of HS. He said the first time he threw on the side in rookie league about 30 other players came up to watch. He's 18/19 years old at that point. He got traded to the Braves for various reasons and told me it was AA ball where the talent started to be fairly serious. Before that, players were often just over matched. At the AAA level, everyone was quite good, some players had "holes in their swing" etc. But nearly everyone could hit well if you made a mistake.
I've heard some say it's a bit easier to hit in the majors because the pitches would be around the plate, while in the minors a lot of pitchers could throw hard but with sparing control. My coach said everyone in the majors is looking for a fastball to hit, they would usually sit on that, and adjust if you hung a breaking pitch.
He said Tony Gwynn was unreal, he'd hit the best pitch anyone threw him. He said their approach was to throw it done the middle and confuse him.