No what I said about the DPS upgrade is not wrong. You haven't calibrated that thing with precision accuracy, on your guide you state it's not very good and at best in 3rd place, that is simply wrong. You are vastly underestimating this legendary and insinuating that the belt is better than it when it gives you no more than a 10% buff to only your next aimed shot at most in most of the time in raid boss fights. Yes Zevrim's is rng within rng, so it's not always gonna be a big boost, but it has way more usefulness then you are implying. Used correctly this thing increases your vulnerable uptime, which means more aimed shots with vulnerable. Hella better than the belt which is only really great on the Eye boss and maybe 2nd phase of Xavius, and Cenarius if you're letting wisps spawn. Not to mention it has the added ability to help smooth out your rotation when you have to move a lot.
Of course it's no better than 2nd place, and that is what I said. That doesn't mean it's bad. It's not. Obviously boots are top, but the belt? Reliable but not actually a big boost at all outside of trash/add phases.
And what do you mean vulnerable uptime isn't a useful metric in and of itself? How do you figure? That makes no sense whatsoever, MM dmg is completely tied in to keeping vulnerable up on your target, target switching fucks with that, as does movement intensive fights. When that legendary procs it's at least giving you 6 more seconds of vulnerable for a low focus cost, it does not require a lot of math to figure out that's a really good dps upgrade...although not reliable, good thing in this case you're only required to keep the hunters mark up to use that bonus 6 seconds to your advantage and that lasts a long time. It gives you options, maybe not all the time whenever you need them, but that's so much more than a mesely 10% dmg on your next aimed shot after you use sidewinders which is all you get out of the belt the vast majority of the time.