I think the personality that gravitates towards Valla is just a toxic player in general. Very rarely will you see the tank or support be the one spewing bile it always seems to be the damage dealer.I'm honestly starting to really hate Valla. She either is played by someone somewhat capable that blows everything up or she's played by some dipshit looking for the FOTM. The first person that I always see complain in a game, and totally degrade the morale of the team, is always a Valla player (assuming there is one).
And yeah since she requires a certain amount of positioning you can get a Valla on your team who's #1 enjoyment in life is being out of position and crushed. Then complain about how it is the teams fault no one backed her up.