I find the way the career is built in Project Cars 2 feels more natural. You progress through promotion categories to world championships. Each category has a prerequisite one.
In forza I understand they wanted to throw in high profile cars early to encourage players, but that can be done via "promotionnal" races or "choose your car" championship
Progression doesn't have to be done from slowest to fastest. In FM7 they could have done it better, but today I think that, with such number and availability of cars, it makes more sense to rank events by difficulty, not speed. The Birth of Grand Prix is higher PI than Sport Compact but much harder to drive.
Still, there's plenty of vertical progression in FM7, which it combines with horizontal progression to form the Driver's Cup. Forza GT comes before Forza P2 and P1, while Formula Ford comes before Indycar and F1. All of these are examples of difficulty related to speed and exist in the same universe as others like Prototype Group Racing being in the last card of events along with Hypercar and later than Forza GT despite having similar PI limit.
You could view having Rise of the Supercar, The Birth of Grand Prix and Early Prototype Racing in the first couple cards as a mistake, but to truly analyze the Driver's Cup progression you must go beyond that, which makes you realize there is an escalation in difficulty that pushes you into progressing further if you'd like, especially with the modern cars.
Also, you are in no way forced to play the harder cups to unlock later championships the first time you go through the career. The game lets you start with early supercars but what if you can't handle them? In such case, you have the option to do a Modern Hot Hatch cup, which is much easier than a Rise of the Supercar one and counts equally towards progression, and come back to the earlier cup when you're more experienced at the game. You don't have to do one before the other. In the age of choice, this is actually quite remarkable.
