You make a good point. At the beginning ranking up was quicker and so it didn't take long to unlock the next event to race in. Now that people are higher in levels it takes quite a lot of time to unlock the next race event by having to constantly repeat the same few events that have already been completed.
I have found myself recently not playing the game for racing (because I find doing the same completed events over and over boring) but to level up enough to unlock the next event to race in
In previous Gran Turismo's the license tests and the cost of the car to compete I found to be enough of a barrier and was actually realistic. If I couldn't complete the test, I couldn't do the races that you had to have that license for, which kept my interest as I had a challenge. Now I have to level up to race in a new event by driving an X2010 around an Oval over and over, hardly a challenge, but I am forced to do so so that I have a fresh event to race in and new cars to win.
Surely I should be spending more time actually participating in races instead of simply trying to level up? Which is why I think people are exploiting this bug.
I hope in future Gran Turismo games they go back to license tests and more events.