League voting is, in my opinion, akin to training wheels. I suppose in a redraft you can justify it, but in any kind of keeper league, managers are going to simply value players differently looking at their team now, and in the future. Multiple times in a dynasty league I've seen people arguing over a trade with half arguing it was unbalanced for one side, and the other half arguing it was unbalanced from the other. Everyone values players differently.
The only reason to have a veto system in place at all is that sometimes collusion does happen. It's hard to judge on an individual basis but if you're in a long running league you can spot patterns. If two teams only trade with each other, that's a red flag. People might know each other in real life with one team being a "farm team" so to speak, trading away its best players to the "MLB" team and going for the championship. That kind of thing is pretty slimy and you need a system to combat it, which is why you have comish veto. A smart comish will be on top of it, and if they have a gut feeling about a trade can talk to each owner individually about it.
Point of the point, a manager should never have to explain the reason he's doing a trade to the league at large. It's insulting.