I loved GT1 and 2 where you had to grind just to buy a turbo or better tyres... but that was when it was actually difficult to win races. Winning now is so easy just using stock cars, that the only point to earning credits is to by sexy cars. And, you not a lot to do that !
So because the Ai has been dumbed-down each year, the fundamental reason for grinding has changed, and so the importance of winning big bucks has been amplified. Unfortunately, the new micro-transaction element is beginning to look very sinister... if I were cynical, I'd say they;ve deliberately reduced payouts, so people will be forced to buy credits.
Of course, they also want want people to keep playing and buying monthly DLCs, so they had better be careful just how far they push this !!! It may well bite them in the ass !