Just to note that the top rivals cars may not necessarily be the best cars for actual racing (particularly in lower classes). RWD builds are a lot more useful in Rivals whereas in actual races the usually sluggish start will often leave you near the back of the field, with your extra pace then been less useful as you have to overtake everyone.
That said, still a very good starting place to work out the best cars though.
Then there is ofc testing the car with setup and sometimes I pick something else, as the best car just doesn’t work for me. I do like to drive cars with handling, not really a fan of sliding all over the place.
Also setups from IsuckAtDriving/Grandma Driving, Valorster and Don Joewon Song usually work for me (that is if I don’t come up with decent setup myself).