Brutal thread.
Let's start here: Martin's drop in prospect status happened before the Twins made the trade. If he was tracking like a star, Toronto never would have dealt him. The public prospect lists take time to catch up. Berrios had value, but not as much as a number of TD posters seem to think.
Next, player development is not a linear process, and it can take time. Miranda struggled for years with making hard contact. Lewis' overly aggressive swing took years to tone down.
As with other prospects that later had breakouts, Martin has some strong MLB-caliber tools, including contact ability and plate discipline. Historically, hitters with better contact ability in the minors are more likely to become big leaguers. Also, Martin is 13/13 in stolen bases so far this year, and has the speed to be, at absolute worst, a decent corner outfielder.
Obviously, Martin isn't going to succeed (even in AA) without hitting the ball harder. If it was an easy fix, it would already have happened. But this is quite literally Martin's job and the Twins' coaches' job. Maybe the swing will get fixed, maybe it won't . . . nothing has changed in that regard.
That's particularly true given that his college career was disrupted by covid and he's played the rough equivalent of one full minor league season. The Twins knew Martin needed work when they acquired him, and . . . they're working on it. We'll see.