To be fair, roster size was more of an issue when Sakurai was basically stuck with the task of balancing characters largely by himself and a select few other testers. And even there, a "manageable" roster size didn't stop the likes of METAKNIGHT from happening.
But now that we've got people who've worked on the Tekken and Gundam Vs. series (whose latest respective entries had upwards of 50-60+ characters to play)? There really shouldn't be any excuses this time. Blow up that roster size and let people who know what they're doing do what they're paid to do, I say.