I'm watching Downtown Abbey, yes, but to me (despite the obvious publicity hooks they've been using) there's not enough similarity between the two premises to compare them usefully. Yes, we see both above and below stairs in both. But DA is centrally concerned with the business of an heir, and the handing of the estate intact (in trust) to the next generation. And there's really nothing comparable to that in US,DS.
I think Julian Fellowes is a clever writer (I enjoyed his novel Snobs, as well as the movie Gosford Park), and he knows the Downton Abbey milieu, but perhaps his plot-invention resources are limited. He's fallen back on soapy contrivances rather often, and I find the prison sequences a deadly weight on the current series.