Any manufacturing process will have it's lemons. Certain years or models will be awesome or horrible within the same manufacturer.
I'd be willing to bet that there are more problem free Keystones than not. People who have trouble free products tend not to be so vocal about it.
I've never owned a Keystone, just speaking in generalities.
And 4 months at a dealership for repair? I'd be upset with the dealer also, not just Keystone.
And one last thought. I can remember when Jayco was generally thought of as entry level cheap junk. Not anymore. Things change