ye you could but that was mostly padding on tentacles at the end and you could even choose when to get mind controlled which gave you a 100% damage buff but in terms of actual useful damage fire mages were still ahead on xavius.

I played it and would spam heroic for fun because you could get insane padding on those tentacles, this is my log from then https://imgur.com/a/h9gveqQ. you can see 44% of the damage during the entire fight comes from nightmare tentacles which was literally just padding and didnt need to be killed at all

sure s2m was super good on xavius but it was also good on everything so xavius wasn't really super special in how strong s2m was compared to how other classes also could abuse xavius