for my opinions? Im going to make this short and painless as possible, okay.
(Background Knowledge) I have played every Forza Motorsport game in history and the 1st, 3rd, 4th and 6th Gran Turismo.
In recent history, I enjoyed playing Forza Motorsport 4 until I decided to give Gran Turismo 6 a try on playstation. although Gt6 had problems with micro transactions, it was jaw dropingly guud and totally blew my mind away from forza for a while. Then I tried Forza 5, but sadly I told my xbox "Xbox!, turn on playstation" and i went back to gt6. Then some game developer named Slightly Mad introduced Project Cars 1 to me. The game was interesting but fell flat on its face with too many bugs and unplayable with the controller. So, the King kong Forza 6 came along and stumped the already crippled Project cars 1 further into the ground. project cars 1 had potential but they procrastinated too long to fix the game; making players angry. Forza 6 couldn't have came at a better time; I even went to pcars forum and laughed so hard about it they kicked me out of the forum and banned that account; I'm still laughing about it lol. Now, Project Cars 2 is here, this game is no laughing matter, okay. Forza 7 is not going to stomp pcars2 into the ground this time. Project cars 2 has delivered for the people who wants to get in the race car and enjoy the simulated experience. this separates them from having direct competition with the almighty Forza, i think it is a smart move because forza 7 seems to provide entertainment to a wide audience of gamers while pcars2 push dedication towards serious sim racers. Now, with Gran Truismo Sport on the horizon and while it will not be considered a complete game to most. Just think of it this way, a half size Gran Truismo will still compete with a Project Cars 2 and a Forza 7. Why, you say? 1) Gran turismo is the sensei of console racing. 2) its going to blow your mind. 3) its only on playstation offering a more premium race experience than anything else out there. 4) its going to make you want to get a playstation if you don't have one already.
So in my conclusion, you would be very happy to have all three.