Just use whatever you want and what works best for you! I don't recommend against DX8.
I just haven't had the time to properly explain it in the docs, since users have the tendency to pick the perceived lowest option even if it's worse for them. So, I've relied on DX8 being known in the community elsewhere to pick up the lack of documentation within the mastercomfig docs regarding this.
I simply only want DX9 to get a fair chance and people to try it and see if it works for them rather than automatically going to DX8. If it doesn't work as well for you, that's totally fine and understandable!