People made this same argument with Yuri awhile back, saying he was no fun to play coz he just spams mines.
I'm not sure if it's quite the same argument with Voltar, since I generally find him pretty boring to play, but at that time I pointed out what wasn't fun for them was still fun for me.
I'm sure some Voltar players would agree.
Fun is of course a purely subjective thing, but skill ceiling is not -- and Voltar's is unfortunately the lowest in the game. No other character is easier to play effectively than Mr. Omniscient Brain, and after you master a few simple tricks (such as maneuvering properly via jumping/hovering, healing wave knockback shenanigans, explosion drone builds) there's no way you can excel over another Voltar through player skill when compared to other characters; you hit a plateau way too fast.
This is the main reason why I prefer Yuri over Voltar, even though I love both characters in concept and design.