I found Daytona easy. I forget what it was that I had to tweak since it's been so long ago, but I got out in front and built up a significant lead that I kept until the checkers. It seems like there was something I had to do with assists to get around the fact that it forces one on, but I don't recall the specifics, but once I did that the AI had nothing for me.
As for the pit-stop challenge, that was just poor game design. I don't mean the challenge itself but the challenge of working up the patience to sit through the same boring pit animation over and over again every time you retry the challenge. I'd have liked the ability to skip past the needless pit sequence to the part where it actually starts to matter. The challenge didn't actually begin until the exit from the pits, up until which you just go make a sandwich or whatever while the game kills time.