Yes, But an iOS app requires a helluva lot more than just the Swift language. For example, Metal has zero support so you have to use ft=cpp and disable lsp diagnostics. And you can completely forget Xcode’s wonderful Metal debugger entirely.
Otherwise swift works just like any other clang/llvm project and the tooling is basically the same.
Yes but most people are not dropping down to Metal support unless they're doing custom effects or developing a game engine. Most apps could be developed outside of Xcode just fine.
Sometimes people add to the discussion by sharing esoteric knowledge because the uncommon aberrations are interesting.
That aside, there was a larger point I was making that was lost in the forest because you poking at a tree. iOS apps are more than Swift. Metal was one example, there are plenty of other tooling components that absolutely suck to use in vim, or just missing support entirely. Bundle management, plist files, custom build phases, code signing, asset previews, canvas previews, interface builder, profiling, and unit testing UI is a bunch of stuff that has nothing to do with swift, sucks in vim, and integral to application development.
Otherwise swift works just like any other clang/llvm project and the tooling is basically the same.