Absolutely correct. Lua, for example, does fine on mobile phones. Python pushes the limit wrt to memory and battery consumption, but if you code conservatively and make judicious use of Cython or native code libraries, you can do OK. Incidentally, Python performance seems just fine for GUI programming on modern mobile phones (based on personal experience). But because of the way you have to package Python/Lua/Ruby programs, it takes a long time to open them. But once they are open, they all do fine (and Lua does fine any way you want to measure it).

As someone developing on Android, I so wish that Google had opted for native code on Android, and a native toolchain SDK, which would have allowed people to use almost whatever language they wanted: C, C++, Python, Lua, Ruby, etc. If that had been the case, I suspect most people would opt to use C or C++ for the backend, and code the frontend GUI in Python, Lua, or Ruby.

And yes, you can use the NDK now, but everything visual has to pass through Java.