"Sure. If I had a heavily restricted system, I would look at LEDE a.k.a. OpenWRT."
That'll be my last resource, it is so easy to build my source code in Debian than in OpenWRT which wrapped the native Linux build system into its own build system, someone might like it, but I would prefer an open environment. What I really don't understand is why could the OpenWRT to make the OS so small but Debian ARM embedded system could not?