I've heard they're short of room in hell
Forget Clefable, Amoongus, Lando, Tornadus, Thundurus, Azumarill, Gliscor, etc. all getting squashed by coverage moves. Lets talk about some of these physical walls that can "have no problems with u-turn".Since when was High Jump Kick an spammable move? Ghost-type Pokemon, Protect users and 10% chance everytime Pheromosa wants to hit doesn't scream a broken Pokemon.
And Poison Jab is not STAB Gunk Shot
And this is the list of Pokemon that can take its STABs wuth little to no effort:
-Talonflame (nerfed), Thundurus.
-Azumarill, M-Charizard Y, Gliscor, M-Pinsir, Skarmory,
-Gengar, Nidoking, M-Aerodactyl, M-Altaria, Dragonite, Volcarona, Zapdos, Togekiss.
Resists High Jump Kick and has no problems with U-Turn:
-M-Sableye, Amoonguss, M-Venusaur.
Also, there's Aegislash, who will be unbanned at the start, who is a complete COUNTER of this thing.
252 Atk Life Orb Pheromosa U-turn vs. 252 HP / 112 Def Mega Sableye: 117-138 (38.4 - 45.3%) -- guaranteed 3HKO
252 Atk Life Orb Pheromosa U-turn vs. 248 HP / 96+ Def Mega Venusaur: 109-130 (30 - 35.8%) -- 36.4% chance to 3HKO
That is not "no problems". You switch in to absorb the HJK, instead get hit by u-turn, they bring in something that threatens you out, and now you have a half dead wall that can't counter anything. This is just like Genesect.
Oh yeah and Skarm
252 Atk Life Orb Pheromosa High Jump Kick vs. 252 HP / 252+ Def Skarmory: 164-192 (49.1 - 57.4%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
You're right that Aegislash completely walls this thing. Buzzwole is actually an incredible counter to it too, conveniently. However, it's quite clear that pheromosa will be very, very difficult to switch into, and very hard to wall. It's very much like Greninja, Deoxys, Darkrai and all of those excruciatingly fast Pokemon that are a terror vs. offense but have the raw power and coverage to be almost as scary to defense.