(3) wasn't relevant (or even really true) in 1977-1983 when Ada was being standardized.
MS-DOS was mostly x86 assembly, Classic MacOS was a mix of 68k assembly and Pascal, CP/M was written in PL/M, UCSD P-System was Pascal, and this leaves out all of the OS Options for the Apple II - none of which were written in C. I'm hard pressed to identify a PC OS from that time period that was written in C, other than something Unix derived (and even sometimes the unix derived things were not C, Domain/OS for example was in Pascal).
If we leave the PC space, it gets even less true - TOPS10/20 NotC, RSX-11 NotC, VMS also NotC - and I can keep going from there - the only OS from the time period that I can point at from that time period that was C is UNIX.
I'd actually argue that C/C++ were not enshrined as the defacto systems programming languages until the early-90's - by that time Ada had lost for reasons (1) and (2) that you noted.
MS-DOS was mostly x86 assembly, Classic MacOS was a mix of 68k assembly and Pascal, CP/M was written in PL/M, UCSD P-System was Pascal, and this leaves out all of the OS Options for the Apple II - none of which were written in C. I'm hard pressed to identify a PC OS from that time period that was written in C, other than something Unix derived (and even sometimes the unix derived things were not C, Domain/OS for example was in Pascal).
If we leave the PC space, it gets even less true - TOPS10/20 NotC, RSX-11 NotC, VMS also NotC - and I can keep going from there - the only OS from the time period that I can point at from that time period that was C is UNIX.
I'd actually argue that C/C++ were not enshrined as the defacto systems programming languages until the early-90's - by that time Ada had lost for reasons (1) and (2) that you noted.