The Crew 2 is still a really good game, and the summit rewards have recently been better than what you get in Motorfest. Boosted parts sets are always worth getting, and if you get an exclusive car, it feels like it has more value as you get it in both Crew 2 and Motorfest. Exclusive vehicles in Motorfest are only 1 in 4 or 5 summits, and they always seem to be slower than the meta options. The one thing you can get in Crew 2 which is absolutely guaranteed to be meta, a boosted parts set with the correct affixes, doesn't exist in Motorfest.
The graphics in Motorfest are better, of course, but the Crew 2 map is more interesting and varied. Some of the gameplay in Motorfest can be more varied, but I feel they've gone a bit too far with some gameplay variants - the chase squad stuff is particularly bad, and the new events where you have to complete quotas of target hits etc aren't great.
Overall, The Crew 2 is still a really solid game, and Motorfest isn't simply a straight improvement on it, much like FH5 isn't a straight improvement on FH4. Even if someone has already completed The Crew 2 and got every car and boosted parts set, it's still possible to have fun doing it all again on a new account.