Partisan issues are not structural problems with the system, they're policy problems with one party. And in my experience people who try to make that argument (and variants, like "both sides do it") are just making excuses to treat the cognitive dissonance of cheering for the bad guys.
 Obvious disclaimer is obvious: not all issues are partisan. There are legitimate complaints to be made about any system of government. Some problems certainly can be structural. This one is not.
Having Mitch be majority leader makes it worse, but you can't solve it by getting rid of him. He's not blocking things because he feels like it; it's his job.