As far as I know -- and I've double-checked this just now -- Yum Brands does not own Wingstop (which doesn't capitalize the "s", even though we all do it automatically). They own "Wing Street", which is a sub-brand of Pizza Hut. Wingstop is an independent publicly-traded company.
Wingstop created Thighstop as a "digital brand" -- essentially, a ghost kitchen run out of existing Wingstop locations. This is a trick that a lot of chain restaurants started doing since the pandemic. Denny's runs "The Meltdown" as a sandwich shop; Chili's runs "Wings & Things"; you can find others. You can only order from "Thighstop" online, but you can add a thigh to combos when you order from Wingstop if you're so inclined.
(And I have not lived in Buffalo, New York, but I have lived in the South -- and California -- and can assure you there are many "mom and pop" wing shops and local chains that…aren't great.)
Definitely some are not great, I can name 3 within a mile of me I won't go to. And some are "sketchy" but delicious. But that also applies to barbecue, mexican, catfish, etc. around me. Just look where the locals go. If there's a line at an unexpected place, it's probably good. But if it's around a college campus, it may just be cheap :).
Yum! Brands owns both, and Pizza Hut, Taco Bell, KFC, etc. The restaurants themselves are owned by franchisees who license the trademarks (and all kind of complicated buy-in and standards).
Yum! Brands made ThighStop to address the wing shortage and keep the association/credibility. It’s actually weirdly transparent: just like WingStop, but thighs. I don’t know if WingStop franchisees got automatic rights to that brand or not. My guess is that it was just a way to keep them afloat.
Now, the fact that WingStop has any cred is gross. I can get better wings from a mom & pop or local chain at any strip mall, or heck, a gas station than wing chains like them, BWW, etc.
I guess America outside the South and Buffalo, NY doesn’t have access to wings that don’t taste like a salt lick. It’s a tragedy.