Hi everyone, i've got my reqs with mainly ice in 45 games.
I think Flutter Mane is only a threat as a Choice Specs because Choice Scarf does not enough damages so it's just a counter to other FMs, Pults and Valiants, Paos with conditions, so it has to predict the good switch to be efficient. I've never faced a CM set and imo that doesn't seem worthy at all compare to a Choice one (even the scarf) as it was mentionned : needs coverage, a sub, a lot of luck with Shadow Ball and hope to not be para/poisonned. Psyshock + Sball it's free Dark types, , Moonblast + Psyshock its free steel types, Moonblast + Sball it's free clodsire toxa spedef (maybe the best one?), and so on…
There are plenty of counters to it in BO / Stall archetypes as everyone mentionned and HO needs to know which mon to sacrifice to have an advantage, same thing than an Iron Valiant, Dragapult, ChienPao, … It is an offensive threat, definitely, but not a broken one. I alway build to have an answer to fast mons: chlorophyl / swift swim, DD, scarf, priorities and hazards to cheap so FM is already solved while i'm taking care of Dragapult (way more options viable so can be much more a threat but not banworthy at all, don't misinterpret).
When I'm reading someone pro ban, everything is in theory but I've never faced those cases and as I said, even a Choice Scarf seems to be better (tho it just cuddles most mons) than CM sets. I can get that generally for mono Dragon and maybe Fight it is pretty complex to deal with FM especially in mono Fairy or in Ghost with Pult + Mimikyu but it doesnt seem impossible with priorities / scarf / hazards. But open to discussion !
For me it's a NOT BAN as I've never struggled against it.