We have a Keystone outback (yes, thor) A 2010 model which we use around 45day/year, about 1/2 time just DW and I, the other have with a 12 and 8 year old grandson, DD and SIL. Has close to 50K miles on it. Still looks almost new, no issues and one warranty issue. Dealer did a 3 hour walkthrough with us when we got it, they had done a great dealer prep and DW found a couple of cosmetic items inside they fixed while we had lunch.
We did have one warranty issue. The coating on the aluminum wheels started to show "spider veins". Keystone replaced them under warranty including the cost to get them balanced.
SIL parents have a 2008 Keystone Cougar 5th wheel. Similar experience to ours.
Are some of the trailers junk? yes, but I'd buy another Keystone again, but ONLY from a dealer that I trust has a good reputation.
