Not necessarily. It could be worse. I'll give you an example. When a major-league pitcher goes down to some of the lower levels for rehab, he inevitably expects to have a bruising ERA. You can check out some of the starts made by big-leaguers in the minors -- or the stories of guys who hit homers of Kershaw on his rehab assignment. There are a few reasons for this. One, the big leaguers talk about how the young hitters come up there geared up to swing, looking to whack the big leaguer and hard, and they're not taking their usual at-bat. Meanwhile, the big leaguer's purpose is to do more than get an out there -- he's trying to get healthy, trying to find his stuff, trying to make sure all of his pitches are right and his mechanics are right and his arm right and all of it for when he starts a game that matters. See, that's the rub. For the minor league hitter that at-bat is what matters. For the pitcher, it's where he's going in another start, or in a week, that matters. It can skew the results.
Instead, look for what the hitter does with his strikeouts, with his walks, how he compares to the league average, and how he compares to the other hitters who call that ballpark home. An outfielder who spends his home games in Memphis and has the same numbers of an outfielder who spends his home games in Reno is a standout, and if you look at the strikeout rate, goodness. Oh, and check out the doubles. Especially in Class AA. If a player hits consistently and consistently hard and has a bunch of doubles -- think Colby Rasmus -- those doubles are a sign of power on the way, power that will arrive as he gets stronger and older and will be there in the majors.