I can appreciate that being on the other side of the fence you would have that point of view. When I was a console player I might have had a similar view. But having been on this side of the fence for a couple years I have a different outlook. AC isn't god's gift to sim racing, it doesn't have every feature you could ever want or every car/track you could want. But what it does do/have it does very well, the cars are unique and feel great, the tracks are beautiful, the physics are addicting, and in my two years I've encountered virtually no bugs or glitches. It just works, and it just feels right.
Comparing the car count to games like GT or Forza is comparing apples to oranges, actually it's probably more like comparing brussel sprouts to oranges. The cars in AC are highly detailed and accurate, each one feels totally different to the other cars and has it's own unique characteristics. It also has a very nice blend of street cars and race cars, low powered cars and high powered cars. I would take 20 AC cars over 1,000 GT cars every single time. Every. Single. Time. AC is different. Kunos is different. It has that intangible "something" that makes it greater than the sum of its parts and any weaknesses are generally balanced out by its strengths. And the dev team is passionate, dedicated, talented, and fun. Plus they communicate with us regularly, and they keep their promises (looking at you Kaz).
As for the DLC, you've all payed hundreds of dollars for a PS4/XBone and possibly hundreds more dollars for your wheel/pedals. What's another $10-20 for some of the highest quality cars in sim racing? Kunos is in this because they genuinely love and have a passion for sim racing/cars, but they also need to make money too, and I feel pretty confident in saying that the money they make from the DLCs will directly benefit all of us in the future, so it's a good investment.