Yes, that's why there's both gc and gccgo (llgo came later). Apart from the rigour of having two independent compilers, they are seeking different tradeoffs. gc is very interested in running fast, and gccgo benefits from decades of work that have been put into gcc's various optimisations.
Does that answer your original statement that you didn't understand why we build our own toolchain?
Well I still don't understand. Russ says it was for segmented stacks, but doesn't explain why those were necessary. You say it was for compile speed, yet gcc and llvm can crank out millions of lines a code a second at similar optimization levels as the Go compiler. Neither of these are convincing explanations.
Does that answer your original statement that you didn't understand why we build our own toolchain?