Custom Race AI seem to improve with each newly added track. From St.Croix to the last update, they've been improved. Tokyo Expresway South Loop, is the perfect example.
I'm not having to catch the leading AI like earlier tracks. I'm getting AI from the back and middle of the grid, progressing forward. It's been pretty cool.
In the video below, I'm using an A45 AMG, tuned to TCR specs.