Coreavc 3.0 does support proper 10 bit afaik (madvr report so at least).
I just like to have fewer filter chain and decrease the risk of something screwing up along the line (and hopefully, speed thing up). Also, isn't 10 bit support depend entirely on avisynth plugins and there are some that support higher than 8-bit (up to 16 bit).
CMIIW.