I don't really like that standing. You are not worse as a GM because you do not want multiple character players, nor are you a BETTER player because you like and use more then 1 character. I could even argue that it makes a you a worse player as you cannot properly convey and add to the story unless you had more then one character. But that'd be the same kind of weak argument. . But as you stated unlit, it comes down to preferences both as a player and as a GM. And in that regard, previous experiences. And every gm has the right to set a rule because of said preference and it's not something anyone should really argue against.
Its also the fact that you are ignoring the metagaming problem. That doenst neccarily have to with a bad player, but because you are writing several characters and the brain will simplify things for you. You WILL oversee certain facts.