I've given my thoughts in the PS room multiple times regarding Haxorus and they remain the same. Maybe, actually, in Zam meta it is a bit worse, because one of the selling points for the dragons is being able to setup on neutral hits for the sweep. While Mence can take an LO Psychic, Haxorus is a roll unfortunately. But while Hogg hits on one of Hax's main selling points, it's not really all of them, and there are a few crucial differences that I find make Haxorus a "different" and sometimes better choice over Salamence.
I've used both extensively, hit something like top 5 on the ladder with an outrageously offensive Haxorus team and have had some of the most success in UU using a Mence based offense team, so I do think I'm probably one of the more practiced users of both DDers to be speaking about it.
Niches Haxorus has over Mence:
- Can take an ice shard - this one is really important. Salamence essentially is not allowed to sweep until you have removed Mamoswine / Abomasnow. That is a MAJOR issue because you have to play super aggressively in order to make your foe actually keep them in to take hits. While, on one hand, this is nice (something like NP Nape can get a +2 while forcing out Mamoswine because it's needed to ensure safety against Mence), it's often really frustrating because the opportunities to DD don't come up super often.
- 100% accurate fairy coverage move - Missing iron tail fucking sucks, but it is necessary on a DD mence set
- Higher attack stat in combo with running adamant, you miss out on some annoying things speed-wise doing so but it's not 100% terrible, and adamant means you can run dragon claw, so you aren't forced into those weird situations where you can't actually sweep because there's still a fairy, but you need to outrage something (say +1/+1 Mence vs 50% Zapdos, you can't kill with Iron Tail but you can't outrage because there's a florges in the back)
- Non-outrage sets have the added benefit of being able to run something other than lum, such as mental herb or life orb or a resist berry.
- More tenuous, but still important to me is Mold Breaker. There was a time when people were running Shedinja / Quagsire on stall a decent amount. Nothing in the world is more frustrating than being unable to break either of those with a fucking Salamence, Mold Breaker makes it a nonissue. Another moderately popular thing this helps against is Rotom-H, which you can EQ, whereas Mence has to outrage again.
- Not weak to SR
- Super super niche but there are a few times when I've enjoyed taking poison from tspikes to setup on something like CroCune, because the lum on Mence is sometimes popped t1 and you have to cross your fingers and pray that you survive another few scalds while you boost
Of course, Salamence has pretty great areas over Haxorus, most notably it's speed tier, which lets it beat all but some common scarfers after a single DD (notably Hydrei). Most in our community love Intim as an ability, I've always been partial to Moxie just because it really plays on that "one free turn" idea, where if a Mence gets a single DD turn it can spiral out of control because you can't sacrifice to it as easily to revenge with a bulky wall.
Point being I think they're different enough, really, despite both being DD Dragons. Not really an apples to oranges comparison, but certainly there are enough merits to Haxorus to keep using it over Mence, though it's harder to fit on teams. People just outright saying "oh it's outclassed by Mence" aren't really considering all the applications, and there are definitely a lot of offense teams that could potentially prefer Haxorus over Salamence. There are also stallbreaking sets which utilize Jolly LO SD and potentially taunt, none of which I use very often so my arguments are mainly confined to the DD sets differences btwn them.
