Both fenders falling off of their own accord in the first 42 miles sounds like they weren't installed properly and probably a warranty item. Breaking stuff moving slides in and out, probably not.
Very little outside of Class A coaches built like houses are "high end" in the RV industry. Look more carefully at most of that "woodwork" and bring a woodworking craftsman/handyman along. They'll enjoy the chuckle as they point out particle board covered with vinyl isn't "woodwork" and they'll probably show you where the most troublesome attachments will be and how to "pre-repair" them so they don't break. Drawer slides with a couple small staples holding them on, etc.
I wouldn't say Keystone is sleazy. They seem from most accounts to be willing to support real warranty issues, and answer their phones, and I've worked with a lot of industries which won't even do that... They do build stuff fairly lightweight and as quick as possible, like almost all of the manufacturers do, and because the market demands it. People want to tow 40' trailers with 1/2 ton trucks. You aren't going to get solid maple wood cabinets with dovetail joints in that market.
If you're looking for what Keystone's opinion is of their quality levels, they show that right on their website. Cougar is in the Select bracket, in the middle below Premium and above Standard.
The reality is, they're all built with virtually the same materials, the trailers themselves. The differences are in quality of things like tables, chairs, thickness of mattress pad, etc... And a few features.