Not a deal breaker, but when you move a player down the defensive spectrum, it means he's now competing for a job with players who are there more for their bat. Guys who can track a ball in the outfield, say, but lack the elite speed/vision/arm to play CF. Better defense in LF may play a small role in roster decisions, but not like it would have in CF. I don't think anyone is saying Rosario should change his batting approach if he's in LF; he should do whatever works best. But his batting skills may not be elite enough, compared to other options of players for that same position. And power will be one of the big difference makers. That's the sense I take such statements as "That means he’ll have to show he can hit for power." Not so much he should change, but can he do it? As for table setters for the power hitters who follow, I'll be happy to see the team solve that problem once it proves to be one.