I can't even see why Grindy would be more popular. Especially from the movie. Johnny Depp looked like a straight up douchebag as Grindy lol. Looked like he was moments away from starting his own punk band in his wizard garage.
We all think "dude changed his looks just to infiltrate the ministry". Nah, I think part of it was because he knows he looks utterly ridiculous.
The guy had some nice wandless magic, but shit has he never heard of a death spell? "I'm gonna lightning zap you repeatedly, Palpatine style".
Voldemorts magic was just more potent in the movies. But this might change.