I played all GT and Forza games and after playing both FM5 and GT6 I can say that I'm fine with the microtransactions in GT6. As far as I can tell (after a few hours) the economy hasn't changed in GT6. I already got three price cars for finishing the first class.
I also haven't seen any "ads" for dlc or microtransactions in the menus. I can still sell cars for credits. The game hasn't been designed around microtransactions like Forza 5.

GT6 has other problems.