How has Disney fallen? Last I checked, they seem to be doing better than ever, and have gobbled up so many IP franchises they look more like a monopoly than ever (Star Wars, Marvel, etc.).

Microsoft sure hasn't fallen either. Windows isn't quite as dominant as before, but MS got even bigger by moving to cloud stuff instead of just relying on Windows/Office.

Sears was never a monopoly of any kind, that I remember. Neither was Kmart, or Wordstar, or GE. AT&T, formerly Bell, was a monopoly and got a huge push from the government in the form of a forced break-up in the 80s. The AT&T of modern times (the cellular company) was never a monopoly of any sort.