SD Haxorus is one of those things that I sorta feel you can't use super hard stall to deal with. Some people, Koko included, have posited that true stall is dead. There's been too much power creep over the last few generations. You HAVE to have some offensive presence. But beyond that, SD Haxorus is just not very good against some more offensive archetypes which tend to rule UU, so it's extremely uncommon. If nothing else, you won't find it higher on the ladder. Heracross is actually dealt with very easily in stall. Mega Aerodactyl and Crobat are the tier's two best switch-ins (maybe outside of PDef Cofagrigus, but Maero and Crobat are way better in general), and they both OHKO with their Flying STAB. Meanwhile, they act as general offensive checks to a lot of dangerous Pokemon in the tier and generally are very good Pokemon on stall.
I'm a little curious as to why you think Aromatisse is easy to wear down, though. It gets Wish, and unless you keep running into people who spam Roar/Whirlwind when you try to Wish/Protect, it shouldn't have that much trouble staying healthy.
On the subject of your last sentence, there are no defensive answers like that in UU. Frankly, that's a mark of a more balanced metagame, you can't just throw a Pokemon like Heatran or Rotom-W on every team and call it good, UU requires a lot more thoughtful teambuilding. For example, Guts SD Heracross is something making tracks in UU right now. Neither Aromatisse nor Granbull can comfortably take a Guts Facade after a Swords Dance, so while either of them work fantastically for slowing down dangerous Dragons like Salamence, you'll need another answer for Heracross like Crobat that can scare it out and make it waste the turns it spent boosting.