But yet you don't elaborate as to what weaknesses they have/don't have and what strengths they have/don't have. At the very core of things, flying and wind are essentially the same in the Pokemon World. Given that there's only a handful of "Wind" attacks so far (a good portion of them already having a type) what's the necessity for it? And how would it change competitive play? How would it benefit competitive play? If you're going to create a type, you'd best be prepared to answer the landslide of questions that come with it, because it is a pretty risky move that carries the consequence of throwing things off-balance. @_@;
And yes, you made it clear that Wind could potentially be SE to rock but...how can anything touch wind? You can't physically touch it, so how are you going to defeat it? If I'm correct, wind is also air, so in that sense, wind would be super effective against every Pokemon in existence bar Ghost types (and certain water types but Pokemon doesn't work like that), since they're already "dead" and I don't think they need to breathe, since Wind types can, to a more extreme, utilize asphyxiation attacks as well as utilize wind pressure and basically control their opponent's breathing and, if you want to get really technical, their entire bodily functions since, assuming that there's oxygen in the Pokemon world (borderlining on "duh" with this), and of course, both Pokemon and people breathe it, that gives wind the advantage already. You're breathing what could potentially kill you, and that applies both to real life and Pokemon.
There are just too many logical fallacies with Wind for it to be possible. And honestly, erosion sounds more like a status effect, because it's something that damages over time, same thing like what Poison does. But since it affects rocks only (and idk whether or not it affects steel types, but I assume so) it'd be fairly redundant.