The libraries that allow Arduino to cross-compile and load the code are quite and achievement. Dozens of boards use the Arduino's IDE. Because Arduino's language is unique, it is language. It may mostly be C, but that's not all it is.
My purpose in asking for the data types is not only for efficiency, but for readability. It could be said that manual bit packing is clever, but its code is ugly, and distracting from the larger program. A compiler could easily pack, in this case, 8 bits into a byte.
The problem comes with code trans-portability and readability when moving to a processor with a larger word length. If there was an auto-bitpacked variable, the same code would just be more memory efficient because the library/compiler would know the word length.
If 1-bit auto-bit packed variables as well as 24-bit integers were integrated into Arduino's...vocabulary--would you avoid using them, or would you use them?