You have two options here, for free you will get at max, 10 new cars, paid you might get those 200/300 cars. If you want the second option then it's normal that they won't be for free, not all of them atleast.
Season Pass is usefull if you want to buy all the DLCs, since you will get a discount. And of course, no one wants a Season Pass right after release, since that just gives the impression they just held back content to sell later. I agree
With the possible addition of more variety of cars, such as classic, group C, etc, etc, many of those won't fit any of the present classes. And there's no point in dividing 500 by 4, since, one, you forgot Gr.B, two, you won't find 125 cars to fit in Gr.1, and three, there are too many good road cars, modern and classic, to just end up with 125 of them.