Actually, yes, this is true and it's something I hadn't considered for newcomers. The 355 Challenge is one of the last cars you 'unlock' because you would generally need to complete nearly the entire challenge mode to earn 30,000 race points. But you have 4 weeks until the start of the first 355 race so it should be plenty of time.
I had a go in the 512 S yesterday in the challenge mode.
The AI seems to be unable to control this car and is all over the place, which makes it fairly easy to earn many RP in no time
After a few races with this car I decided to change car, because it felt almost like cheating.
Of course if you want your 30000 RP in a quick way this might be the way to go, but I like it more the hard way.