if he were ever proven to be capable of fully harnessing franklin's power then we could say onslaught. assuming that is the version being discussed here... the standard mags\xavier blend wouldn't have much chance i don't think. onslaught was...hard to gauge though. we didn't really see what his evolved energy form could do, so most things onslaught related become speculation in a lot of ways. at least in most threads where a very specific showing for him isn't the topic. /shrug
https://m.imgur.com/ORvzAcu
http://i.imgur.com/F2dd4uB.jpg
And this was before he dipped into Franklins power.