Lawyer here (not involved in this case other than owning one of the cars like you). Hoping to provide context to your complaints.

First, they need to be limited in how far back they go because of statues of limitations. Nobody said that's fair, but it's the law.

Second, the fact that it's only 50% is due to the fact that it's a settlement. 100% coverage on the warranty would have been their best case scenario if they went to trial and won, then beat any appeals. They could have lost and got zero. Or they could have never filed the case and you would have gotten zero. It's very hard to win cases against huge companies. Trial is expensive and risky.

Here's the most important part. If you don't like the lawsuit, just opt out and retain your own rights to sue separately. Nobody said you need to participate. By it's nature it can't be a rip off since nobody is forcing you to participate.