Jean-David Beyer wrote:

It was about that time that the BASIC
OS-Language came out.

Misunderstanding. BASIC was never used as an operating system language.

BASIC was prevalent in RSTS/E (at least to V9 when I quit it) and one
could execute BASIC statements at the command line, and it was used in
many utilities, but the OS was coded in assembler.

Trivia: utilities were so novel that a comment line in part of the SORT
utility was:
1024 ! WOW I FINALLY GET TO USE XOR

Wow. Talk about naive.