Just because you sell more of something doesn't mean much. Sell something cheap enough and you will sell a lot.
If you hang out on the Airstream forums you will read plenty of things go wrong. No hush hush. But 70% of all Airstreams made since the 1930's are still in operation. That says something about the brand.
I agree there is always someone having something negative to say about a particular brand. If you read enough of the comments, you can establish a pattern. All RVs have problems. They are made by human beings, and as such, are imperfect. But some have more problems than others. And some last a LOT longer than others.
As the saying goes, "you get what you pay for".