The ai on forza are very different sandals. It uses a feature called drivatar. Basically it memorises your friends driving styles and uses them as ai. Not just a computer programmed racing line. These ai will brake late and take strange lines. They will block you. They will nudge you. Makes for a challenging race before you even start adjusting the difficulty.
It does take a while to work out the tuning system for new forzas. They always refresh the algorithms.