Except nobody cares about vectorization of your printf("Hello, World\n") or other 12-character strings. Vectorization here would in fact be a waste of build time as well as object output size, and the runtime performance would be not measureably different, possibly even slower in some cases. It's a total waste.

When you're processing actual buffers full of text or binary data, and performance matters, of course you are not advised to use an in-band signaled sentinel like zero-terminator is. Use an explicit length for those cases.