Playing GT7 you will still need to grind them races that have the better payouts over & over, if you want one or all of the high priced cars in the game. Playing GT6 I did not buy all the 20 million credits cars in the game only 2 cars, and I had to grind for them and the other cars I needed for my garage.
GT Sport is not a numbered game, but it was good for earning credits with the amount of cars in the game
.
I expect GT7 game economy is going to be like GT6 game economy when the game server was online, and you still need to Grind to earn credits by doing the same race again & again, to buy them unicorn if you want. For GT7 you be able to buy the cars at the PS store so you don't need to Grind for them, but if you say no to the PS store well you have to grind.
For GT7 you may win a lot of cars by winning the events anyway. So whatever happens in GT7 just play the game whether you play for 30 minutes or 2 hours a day, and remember this just because you can only play for 30 minutes a day and you blame the game for a poor economy is a very lame excuse.