Caveat of us not knowing the details of character balance yet, yeah, Sonic definitely might be. Thing is, however fast Mega Man's projectiles are, he needs space between himself and his opponents if he's gonna get off more than one, two, or three shots. If a fast opponent gets past those, they have essentially an open target who only possesses a single melee-range uppercut and a grab (as far as we know). If he's facing a slower opponent, or can continually knock his foe away and pepper them while they recover, he'll be in better shape.