I'm #1 on the ladder without Skuntank or Inner Focus, saying it is "required" is ridiculous. It is definitely a top mon, possibly the top mon, but there are ways to deal with it. I'll share some of the ways from my team:
Fake Out Ambipom hits it hard and will usually force it to flee (which will often let you punish the switchin accordingly with Thunderpunch or Pursuit a low health Skuntank). Feint is so weak that Ambipom can switch in plenty as long as it comes in on a Feint or Sucker Punch (this is not that hard if you aren't too obvious, and if they get overzealous trying to catch your Ambipom it is GG for their skunk).
Gengar and Froslass are both immune feint, outpriority sucker punch with SP/Ice Shard, and flinch or freeze Skuntank that tries to crunch. There is some prediction here, but I would give the advantage to the ghost types especially if sashed so they can take sucker punchs and reciprocate with a freeze.
Depending on Skuntank's EVs Mega Scizor can completely stall out feint, taking around 3%. If it catches a Silver Wind boost (this isn't hard at all) before or while Skuntank comes in it can also outspeed slower skunks with a Feint of its own (this actually ends up being a great move on Scizor), or BP if Skuntank wants to switch moves. If Scizor isn't mega it can probably run leftovers and be untouchable by Feint, or Rocky Helmet just to be cruel.
I've been able to take out Skuntanks by simply staying in on them. As people say, a skunk will often try to predict the switchin to a ghost or scizor or inner focus mon, so consider just staying in and firing off another attack. As long as you have a Skuntank counter alive it doesn't actually have to come in to force him away from feint, and one freeze is all you need from the likes of Greninja or Lapras. Some thought, mindgames, and switching around really can work wonders considering feint has such a low offensive presence.
I may not, but 90% of teams run Lucarios and Dragonites anyways, which are solid pokemon that as far as I know will beat Skuntank 1 on 1. Again, see what I said about Ambipom - feint has such a low offensive presence that you can afford to take a few just to make your switch in more unpredictable.
There are surely plenty more ways. Feint Sharpedo is one idea I had that should be able to lay some solid hits on Skuntank, and speed boosted bite and aqua jet make sure Sharpedo can actually put in work against other teams. There is no doubt Skuntank is good and there is no doubt it can beat a lot of pokemon. But I designed my team before Skuntank started appearing and it still does fine against it (only change was adding Feint to Scizor). It isn't some threat that will require you to use otherwise unviable things just to fight it, or that only has a select counter. I don't even think I've seen a team that didn't run at least one of: Dragonite, Lucario, Gengar, Skuntank.
Edit: I'm not even sure what I'm more afraid of, Skuntank or bulky Lapras with AP/Rest/Ice Shard/Iron Head or Ice Beam. My team isn't as hard-hitting as a lot of other teams I see but Lapras is just an amazing wall.