There's still a sizeable number of Fury parses in Mythic (public logs only, yeah, but we make do with the sample sizes we get). And there, where there's less cleave padding going on due to mechanics, Fury is pretty close to Arms. Yeah, sure, if you're Method tier you should go Arms. There's, what, 5 or 10 guilds at that level or even close to it in the entire world? For most anyone else, including the vast majority of Mythic's population, you can very well make Fury work. It's not an EN situation where Arms was way above all the other specs and Fury was almost dead last doing 60% of its DPS. And I still played Fury in EN because fuck Arms.
Plus, OP seems to mainly worry about pugging, which obviously doesn't happen in Mythic. And anyone who decides to stack Arms instead of Fury in a pug thinking there's a massive difference is a useless moron.