By justification, I simply meant justifying the exclusion rather than the logic behind the methodology. Sure it makes sense that some locations could be reachable only if you have a way to fly, but like you said in fact, it doesn't make sense that an area in CoC can only be reached with a wing TF with no other alternate method. In fact, it would actually make more sense that more than one exact and specific option exist. Granted, it wouldn't be the first case in CoC or the mods. Personally, I don't even like how the two main "towns" are corruption locked, though they are far more reasonable considering they require passing a corruption check only once and the whole point of both existing are in fact meant to serve as alternate options of each other so that at least one of them is always available once found.
I'm fine with the idea of a TF-locked area, BUT I feel there's gotta be a way for characters without such specific TF to at least have a chance at getting there. Even maybe having some option where if you have no wings, any of your camp residence with wings could perhaps suffice instead. That hot air balloon idea could be that you pay some schmuck to borrow his/her balloon for gems...or other stuff.
Or you could just try and jump the poor thing and make yet another creature your personally punching bag and get there for free!