Did you even realize that...people that builds cars with 350 + score, builds them with a purpose, to beat records on a specific kind of track, join URL or simply discover a better dyno setup...
What you can't realize is...the top drivers spend a lot of time in the same track, working on setups and honing their skills on that track. Going on quick race is a setback, you will end up racing on a drift track, a drag, a speedtrap or
Ambassor Ridge long boring track with many laps...
Most cars becomes very competitive arround 350 score (of course with a decent dyno setup), and you can start to take on cars with higher score
(Example: a 350 scored C/B class car, can take on an 450 scored B/A Class car on a track that requires more steering/braking techniques than acceleration/speed)
Once that becomes possible, the driver masters few difficult and fun-to-drive tracks and slowly increases the car's performance, pushing on the limits of their driving and their setup knowledge..and sincerely? driving on quickrace isn't attractive anymore, even if you get a bit more of cash / RP
I'm not saying that quickrace is useless though...it's a great feature to find matching opponents, it works better on lower car scores because at lower scores, The Car factor is very limiting, since they're slow af and driving ability won't be as influental as the car's power. it's harder to upgrade your low-scored car only on custom race, quick race is your best choice after time trial and magazine.