For the most part, either shit aggro decks or decent walls are what holds together a UW fliers strategy in most limited formats it exists in.
Aggro decks are the default in my environment, and even the control decks have creatures that they'll attack you with (As lucas has proved repeatedly!)
A wall, at it's base is (And there's a lot of mental shortcutting here) Immolating Glare, but you can switch it's target later (by blocking a larger creature).
Aggro decks won't want it where they would want something like glare: even if you're not being attacked all that often, it gets a creature off the board. A wall would just make that creature not attack, which stalls your plan of attack
UNLESS all your creatures have flying, and they can't block anyways!
Don't get me wrong, I love Wall of Cantrips (Both of them!) but I recognize their power: they're both such strong pure control cards I'm not really sure I should be including a second of either, and it's frustrating that there IS actually a deck that wants both of those, (Skies) but it's never EVER green and it basically has to slam wall of omens instead of being able to wheel a card nobody else wants like it's supposed to do with these narrow psudo-removal spells. Kinda the same reason we put condemn in, right?
Maybe this is all talking out of my ass and this hypothetical wall I want to add will just be 14th each and every time, but I do have the benefit of a largely expanded possibility space, so there might be something that works
Mnemonic Wall has been great and well-loved here. Use the Theros one for the better flavour text.