Right now the metagame is playing with waluigi wiggler, but the lack of speed in scooty is nearly negligible.
Indeed, looking at current WRs, it seems that the few tracks where scooty hasn't appeared yet are mount wario and wario stadium, 2 big frontrunning tracks you could say. yet I tested scooty in these two tracks. and I was surprised by the result as it was neeearly a tie on both. but it's not really what matters the most.
What people are arguing against the scooty is its lack of speed in the first seconds of the track. but... let's buster some myths.
The only place where you might get bumped off if you play against a wario wiggler is on Sunshine Airport's first turn. Tracks like rDKJ, dHC and MW are not what could make a scooty user scared (especially dHC). rWS is a special case because you need to take only the first 2 coins (if you take the 4, you might get fucked too). those 2 coins are enough as you only lose about 0.220s per lap (considering you haven't used the coin that you got in the first itembox). Moreover, I would definitely say that scooty even is needed in some tracks, such as Dragon Driftway, where the NISC is completely free with scooty (and you don't get bumped off at first turn, trust me).
Not only scooty's base speed is not a problem because of its MT stat, but it also have one of the best hitboxes of the game for online mode. you just control your speed in an easier way than the wiggler lets you do so, and you dodge more items. its acceleration stat makes you get your normal speed in less time than a wiggler after you get hurt by a shock (for example). it did save me some times. strats are easier with it most of the time, and some NISCs are free (SGF, dDD). Though, the Mute City's one is kinda harder.
Then, what's the matter..? well it's, in fact, not about the stats, but more like about the confidence you get playing x combo.
Waluigi wiggler is something that everybody uses because it proved to be good enough by many great players. And that's the difference with scooty: not many people gave it a try. Yet there are still very good players using scooty, like Robel, Cynda, Nitroco, Sebas... So, if you don't feel confident about playing with it, then don't pick it. Otherwise, just keep in mind that it does not suck and you'll do good with it.
But don't forget that changing wiggler for scooty won't make your skills highly increase. Even if it does, it'll take some time. The differences are so negligible that it's just about the... confidence. But I already said that, right?