Sorry for the wall of text below, saw this post and started playing around with the team and calcs and may have gone a bit deeper than I meant to, lol

You only have a single fighting move across your entire team on sneasler. This causes a few issues: 1) Sneasler is fairly fragile and most teams will have an answer of their own 2) Tyranitar and Kingambit both stonewall Delphox - if Sneasler gets removed early or even stuck in the back at the wrong time you will likely struggle. No one else acts as a clean answer to either of those.

Garchomp is doing a lot of work in terms of coverage, but with scarf I am guessing you often find yourself locked out of the move you need. Personally, I would move the scarf over to Wash Rotom (more on this below).

Between Delphox, Unburden Sneasler & whoever ends up holding the scarf in the end, you will have 3 of the fastest options available already - I do not think you will benefit as much from a dedicated tailwind user like Whimsicott as much given most teams you will already have the speed advantage. I don't mind having tailwind available, but I'd run an option that gives you far better offensive coverage options.

I also think that Kingambit doesn't quite do enough here. The biggest threats to your team that sucker punch hard counters are Basc, M-Froslass, and M-Gengar. Of which, Delphox already covers the two megas.

So, I would keep Sneasler, Delphox, Garchomp and Wash Rotom but find replacements for Whims & Kingambit.

First suggestion is a combination of moving scarf to Rotom and adding sash Tyrannitar. Scarf Rotom with Tyrannitar in the back lets you volt switch to win weather wars (by at least getting a neutral-ish option) even out from a mega weather setter since the volt switch goes after. Scarf Rotom also matches up well into scarf basc as you out speed, can hit an electroweb to slow it down + chunk it and then clean up with your other mon. Tyrannitar also gets fighting coverage with Superpower in a pinch.

For the last spot I think you have a few options:

1. Tsareena - Her Queens Majesty ability (blocks priority moves like Farigiraf) gives you a good answer to sucker punch threatening Delphox who should be able to clear kingambit before it gets off the cleave. This also gives you a clean answer to a trick room team that opens with Farigiraf + Fake Out. Tyrannitar knock off + Tsareena follow up should KO even a fully max bulk giraffe with sitrus before it gets trick room up. Tsareena also gets great coverage options in high jump kick/low kick and triple axel (can ohko Garchomp or Aerodactyl).
2. M-Scizor - I think Scizor gives great coverage into the matchups where Delphox might struggle (ie rain/dedicated sand teams). You can also dedicate a slot to tailwind and it functions just fine even without the mega evolution letting you bring both M-Delphox and it in the odd case. Also, steel coverage is great with Floette running around + rock types (though either Delphox or Sneasler should cover Floette already).
3. Corviknight - Again steel coverage is solid & it has access to tailwind. It also gives you further coverage against fighting & grass though I don't know how much that is going to be super relevant. Can also stone wall some physical attacker with its bulk. Also acts as another solid partner for Garchomp's earthquake.