And I am saying you don't need to rely on any of that. You can just ship it yourself (statically link, or use LD_LIBRARY_PATH). That's what Windows applications that rely on GTK or Qt do as well, and it works fine, which works well, and it works fine for Linux too. The basics (libc, libX, etc.) are stable, and the Linux kernel is stable.
And this is what Windows does too really, with MSVC and dotnet and whatnot redistributables. It's just that these things are typically included in the application if you need it.
It's really not that different aside from "Python vs. Ruby"-type-differences, which are are meaningful differences, but also actually aren't all that important.
Available API means the whole stack, everything needed to write applications end to end, regardless of their purppose, not CLI and daemons.