GCC is free and open. Clang is free and open. BASIC is commercial, proprietary, closed-source software.
The "bedrock of computer science" is machine code, or if you're not a fan of reading and writing hex values or flipping physical switches on your Altair, then assembly. Everything after that is an abstraction.
C isn't suitable for most K-8 students. Explain malloc while I handle PRINT, INPUT, PEEK and POKE. We'll meet at memory registers and see whose student feels more confident.
You've created a layer cake of abstractions with your OS, advanced filesystem and C compiler (plus libraries). I presume a mouse and metaphorical desktop "icing" are included.
Consider DONKEY.BAS: https://github.com/coding-horror/donkey.bas/blob/master/donk...
Perl is more friendly and forgiving than that.
While many 8-bit versions of BASIC were derived from MS BASIC (1975) it was hardly Microsoft’s baby. Atari BASIC for example has zero to do with MS. Neither does TinyBASIC
BASIC itself is absolutely free. Certain implementations are not.
It hasn't been machine code for at least two, maybe three decades.