Some food for thought:
So I was reading the OU Council's thoughts on Phero, and they stated 6 counters:
Tapu Fini
Toxapex
Clefable
Alola-wak
Gengar
Tornadus-T
Let's see if they are really counters or not:
You see, one of my teams has a choice specs sets of FBlast/IceBeam/
T-T:
252+ SpA Choice Specs Pheromosa Ice Beam vs. 248 HP / 8 SpD Assault Vest Tornadus-Therian: 244-288 (67.5 - 79.7%) -- guaranteed 2HKO (Tornadus-T can't even switch in)
252+ SpA Pheromosa Ice Beam vs. 248 HP / 8 SpD Assault Vest Tornadus-Therian: 162-192 (44.8 - 53.1%) -- 30.5% chance to 2HKO (Lol, even without choice specs it still can't counter it well)
4 SpA Life Orb Pheromosa Ice Beam vs. 248 HP / 8 SpD Assault Vest Tornadus-Therian: 161-190 (44.5 - 52.6%) -- 19.9% chance to 2HKO (Yeah...)
Gengar:
4 SpA Life Orb Pheromosa Ice Beam vs. 0 HP / 0 SpD Gengar: 140-166 (53.6 - 63.6%) -- guaranteed 2HKO (Need scarf! (seriously tho, are you gonna use a scarf user to deal with phero? sooo unreliable))
252+ SpA Choice Specs Pheromosa Ice Beam vs. 0 HP / 0 SpD Gengar: 213-251 (81.6 - 96.1%) -- guaranteed 2HKO (Lol, add some chip and bye bye gengar)
252+ SpA Choice Specs Pheromosa Hidden Power Ground vs. 0 HP / 0 SpD Gengar: 284-336 (108.8 - 128.7%) -- guaranteed OHKO (Yeah... if you invest more in bulk then you're gonna be too slow and specs HP ground 2hkos every gengar unless you're running 252/252+ AV (lol) and you also need SR outta the field so yeah)
Toxapex:
252+ SpA Choice Specs Pheromosa Hidden Power Ground vs. 252 HP / 24 SpD Toxapex: 164-194 (53.9 - 63.8%) -- guaranteed 2HKO after Black Sludge recovery (Wow, even toxapex falls to the mighty phero, not to mention that it is passive and it is destroyed with dugtrio)
252+ SpA Choice Specs Pheromosa Hidden Power Ground vs. 252 HP / 252+ SpD Toxapex: 126-150 (41.4 - 49.3%) -- guaranteed 3HKO after Black Sludge recovery (This set narrowly avoids a 2hko after SR, but just add some chip damage (okay I admit it is a little hard with regenerator) and you get carried through)
Alola-wak:
252+ SpA Choice Specs Pheromosa Hidden Power Ground vs. 0 HP / 4 SpD Marowak-Alola: 270-318 (103.4 - 121.8%) -- guaranteed OHKO (LOL!)
252+ SpA Choice Specs Pheromosa Hidden Power Ground vs. 252 HP / 252+ SpD Marowak-Alola: 188-222 (58 - 68.5%) -- guaranteed 2HKO (still 2hko)
252+ SpA Choice Specs Pheromosa Hidden Power Ground vs. 252 HP / 252+ SpD Assault Vest Marowak-Alola: 124-148 (38.2 - 45.6%) -- guaranteed 3HKO (Okay, you can take a hit now, but suffer from a suboptimal set and suffer from the fact that you're still 2hko'ed after SR, Oh yeah and you can't constantly switch in)
There's also HP electric
Tapu-Fini:
252+ SpA Choice Specs Pheromosa Focus Blast vs. 248 HP / 16+ SpD Tapu Fini: 120-141 (34.9 - 41.1%) -- 71.1% chance to 3HKO after Leftovers recovery (nice 3hko there just ad some chip damage and boom, yeah this one counters choice specs phero but not very well, and I can troll you and run)
252+ SpA Choice Specs Pheromosa Hidden Power Electric vs. 248 HP / 16+ SpD Tapu Fini: 160-190 (46.6 - 55.3%) -- 17.6% chance to 2HKO after Leftovers recovery
(Yeah)
Oh wait, Phero learns poison jab!
252+ Atk Pheromosa Poison Jab vs. 248 HP / 248+ Def Tapu Fini: 132-156 (38.4 - 45.4%) -- guaranteed 3HKO after Leftovers recovery (Damn, a 3hko again even with max max max defense)
252+ Atk Life Orb Pheromosa Poison Jab vs. 248 HP / 248+ Def Tapu Fini: 172-203 (50.1 - 59.1%) -- 76.2% chance to 2HKO after Leftovers recovery (lol)
252 Atk Choice Band Pheromosa Poison Jab vs. 248 HP / 248+ Def Tapu Fini: 180-212 (52.4 - 61.8%) -- 98.8% chance to 2HKO after Leftovers recovery (lol)
Yeah...
Clefable:
252+ Atk Choice Band Pheromosa Poison Jab vs. 252 HP / 64 Def Clefable: 356-420 (90.3 - 106.5%) -- 43.8% chance to OHKO (TF okay let's get real)
252+ Atk Pheromosa Poison Jab vs. 252 HP / 64 Def Clefable: 238-282 (60.4 - 71.5%) -- guaranteed 2HKO after Leftovers recovery
I mean, sure they may counter most Phero's variants but the widely common Choice Specs deals with 4 of those so-called counters, and the rare Choice Band set deals with the other 2 (I also think the Choice Band set also deals with Torna-T), heck, even the LO set deals pretty well with Clefable and Tapu Fini, when you see a Phero it is a guessing game until you figure out its set, seems familiar? (*hint metal bug hint*), and there's no surefire counter to Phero that can counter all of its sets, I would mostly go with Toxapex or Tapu Fini, but if my opponent runs a choice specs set with HP ground and sees that I have a Toxapex on my team, it is really obvious that I'm gonna switch to it and then my so-called-counter becomes just a dead-weight, so I've just fitted a passive pokemon on my offensive team to deal with Phero and it failed in its role, how nice...
The OU council in the OP summed up mostly everything nicely, I would recommend reading their thoughts again.
Oh yeah, one more thing, Scarf Pheromosa late-game is a whole new topic and don't even get me started that Phero learns U-turn
Edit: Admittedly defensive Volcarona deals with Pheromosa quite well, but it dies to SR, rip.
My point is that Pheromosa needs to be banned because of the combination of its stats, movepool and ability.
NOT because it's "versatile" or "unpredictable."
Starmie can run bulky defensive sets or pure offensive sets, be a spinner or a cleaner, run bolt beam or just its stab attacks, have natural cure or analytic ability, hold leftovers, life orb or focus sash, or even set up gravity. It's versatile and unpredictable. But it's not ban worthy.
Ban Pheromosa but for the right reasons. Not because people predict it wrong and get butthurt.
I wouldn't ban mosa for its stats, movepool and ability only, I mean a predictable mosa is manageable even with such stats, movepool and ability. It is just the
combination of its stats, movepool, ability,
versatility and unpredictability makes it banworthy, Starmie may be unpredictable, but its stats aren't that good, Phero tho...