Yeah, they've never been #1 and their highest rank ever was #2. I used to work for a different automotive aggregator company like Autotrader.com that wasn't an EMD and it took two years to get to position 2 for the term. The company has since gone out of business, but I can tell you if you jump into the links and everything on UsedCars.com the different in link profiles between them and the other competitors is astounding. Autotrader, Edmunds, Cars.com, KBB.com all have much more robust SEO, so the EMD helps them quite a bit (though as you pointed out they are a high quality site still).
I agree mostly on the brand thing too. I have my own branded site ListHere.com that's for classifieds and like the name more than if I could get classifieds.com or what not, but I also run a bunch of EMD's for affiliate stuff that rank well and convert well since they're focused on singular products. Really depends on what the purpose is I suppose. For me, List Here is a "legitimate" business opportunity, while the affiliate EMD sites are really just short-to-mid term incremental revenue, definitely not something to quit the day job for.