LuaJIT interpreter which is _faster_ can be used on iOS. So you would use an immature language everywhere because you can't use the fastest implementation on one platform (iOS), when infact, the LuaJIT interpreter is the fastest interpreter of any dynamic language on all platforms.
Wonkiness is not a substantive claim. How do class systems break because of it?
I consider Lua's type system almost mathematical in its elegance. For my taste, Lua is the penultimate dynamic language, held back only by the unforgivable Wirth-style indexing from 1.
The one place where I simply must correct you is in calling tables inefficient. LuaJIT's implementation, as interpreted, is demonstrably among the fastest general-purpose container classes in widespread use.
LuaJIT is state-of-the-art even without the JIT. A lot of people miss this and go down various rabbit holes only to come up with something that's significantly worse. Personally, given what I just described, I don't see how Gravity compares at all favorably to Lua.
Lua is pretty simple and elegant, but has its woes on being too flexible and wonky (especially with nil and global variables). It also doesn't support OOP syntax directly, so everyone started to create their own wonky class system, which broke easily because of Lua's wonkiness. Gravity seems like a good embedding language packaging a nice OOP syntax with a lot of syntactic sugar (such as properties and access specifiers), so I think some UI/game developers would choose this over Lua.