Its technically an online game as its connected to Xbox Live, even though you can go Horizon Solo.
If you're having trouble beating AI then I am unsure how good your driving is - Highly Skilled is the lowest you should have the drivatar difficulty to complete each seasonal, and it should still be easy enough to offer a challenge but not that hard you always fall behind. Depending on vehicle class for event, sometimes you'd be a good 5 to 10 sec ahead of everyone.