There is no benchmark. As a species, we don't even know know what a good programming language is, let alone how to reliably develop one. This stuff takes time, and we're all learning it together.
I like to compare this to real world cathedral building. There are some cathedrals that are literally taking centuries to build! It's OK if the important, but difficult thing takes a long time to build.
If you keep up the development pace you're going to approach stability. Unless you're in a manic spiral of rewrites.