Like other have mentioned, I really don't want either of the proposed options.
I want something that has a lot of different disciplines in it across all 'tiers' within the discipline, but I want each discipline to be properly fleshed out with appropriate rules, manufacturers and event schedules.
We don't need 300 cars to make this happen, we just need developers to be more selective of the cars used.
What I'd like to see is a sim with a proper career mode with realistic career progression. The sim could launch with GT and Open Wheel disciplines covered as a base line. So that would include Formula Ford, F4, F3, F2 and F1 for the open wheelers, and then some lightly modified GT cars, GT4, GT3. This base sim would include a flexible weekend scheduling system that allows the user to create a race weekend appropriate for a variety of different series. Different types of qualifying (single car on track, single session for all cars, multiple sessions in groups, multiple sessions of 'elimination' style, top 10 shootouts, etc), different types of race weekends (one main race, handful of short heat races leading to a main race, 2-3 feature races that make up the 'round' on the schedule, etc. Sprint race formats or endurance formats and everything in between). It would include multi-class racing; with different finishing positions and championship points for different classes within a race, as well as overall classifications. It would include full dynamic weather and daylight and driver changes, and on-track racing rules appropriate for the series. Each category would be fleshed out as in real life; FF with 2-3 different chassis, F1 with ~12 and the other open wheelers would be spec. GT classes should have minimum 5 different manufacturers per tier.
Once that's launched, the first 'smaller' DLC would come with Prototype classes (LMP3, 2 and 1), and a full touring car ladder, along with a few more circuits.
The first proper expansion would add oval racing, again with a full tier; 'Thunder Cars,' Latemodels, Super Late Models, Trucks, Nationwide and Cup series along with a generous smattering of oval circuits ranging from the tiny grassroots bullrings to the super speedways and everything in between. This expansion would add in oval-specific setup features to the cars that would have them in real life. Additionally it would add Indycars (and Indy Lights) to the open wheel ladder. This expansion could exist standalone, or combined with the base game.
The second expansion would add rallying and dirt physics. A handful of rally specs for a proper rally ladder and at least 6-8 different countries with at least 10 unique stages each, plus reverse. It would add snow to the weather options for some rally stages. This expansion could exist standlone, or be combined with the base game.
The second 'smaller' DLC would release with Rallycross, and several rallycross circuits. This would require the rally expansion.
There's a lot more detail to this in my head, but basically that's what I want to see. Get a good full mix and match game and career mode, but with very focused content.