It took way too long and I had no reason to do it, but I beat all the tracks on hard, got the banana car, and beat all of Dani's times! A lot of shortcuts were involved, but this was soooo difficult with how good the AI and Dani's ghost are and how hard drifting is!
Here's my PBs, all with the banana car!
Dusty Desert - 0:41:63
Funky Forest - 0:46:29
Sneaky Snow - 1:06:97
Pink Plains - 1:17:97
Akina Downhill - 1:53:18