They've both been pros long enough that their current will be close to their peak.
B isn't a major league player. A is a bench player, could even be a platoon CF although he'd be about the worst .310 hitter you can imagine, with no power, no walks, and a ton of caught stealing.
If you routinely veto trades that are something for nothing, no matter how mediocre the something is, you should veto this. Otherwise let it go.