I thought it'd be super fun to make them in the game, and I hadn't seen anyone else add them. Besides the hair not being fully accurate I think I did pretty well! They may be my favorite mii on my island tbh, and a top 3 fav of the show.
If I'm being totally honest, the imagery and sequences with the Hellcharger are so much cooler and more meaningful than anything with the motorcycles. The way Robbie can stand on top of it when it's going, teleport to it, and morph through it, it is the most badass thing ever. And it's relevant to his character, since he's a mechanic and yk, he died in it. Comparatively the hellcycle doesn't have as much meaning after Marvel forgot Johnny was a daredevil and Danny doesn't really have any connection to bikes (Unless you count him being a paper boy as a kid I guess)
On top of that, it just being a car leads to more characters and more variation with how its used. Like when Cecil the Ghost Hacker gets trapped in the trunk with Eli in the Unbelievable Gwenpool crossover, or when Fantasma rides with him in Spirits of Violence (terrible comic but I'm glad it brought Robbie back)
Overall I think the Hellcharger has a lot more variety and striking imagery. BTW this comes from someone whose favorite is Danny so this isn't biased.