The problem is not staff picking a character.
The problem is Headwiz XYZ takes Batman. His wife takes Catwoman. Their 4 friends take Wonder Woman, Superman, Green Lantern, and the Flash.
All while Headwiz XYZ absolutely knows for a FUCKING FACT none of those people are actually going to play the game much. But it's his wife, their friends, etc, so he lets them anyways.
Oh and then Staffer A wants Nightwing, and his two friends want Batgirl and Zatanna, to play with him.
Staffer B wants Aquaman, and his girlfriend takes Mera.
Wow, suddenly your game is already in the fucking D-List, especially for female characters.
I mean, if you stop at "staff picking characters" in this scenario, you only have Batman, Nightwing, and Aquaman picked. Not exactly the end of the world.
The problem is when all their friends also get first dibs.
And god forbid if they're snatching alts immediately too. Even 'second tier' ones, because they're going to snatch all the 'top' on that tier too.
Edit : I will say, that for whatever reason, Comic MUers make the most RIDICULOUS fucking fuss about NEEDING alts. It's obnoxious, but the sad facts of MUing are "big who list = more players will stick around when they log on to look", and a lot of people will NOT hang around if they aren't allowed to squat on 3, 4, 5 characters. So you're shooting yourself in the foot twice on this one issue if you don't allow alts.