Well, I can tell you for sure that the standard for high end productions in theatre is Dataton Watchout. I have programmed five shows on Broadway that use Watchout, including Rock of Ages, Lombardi, and The Pee-wee Herman Show, all currently running. In addition, Sondheim on Sondheim, which used 54 screens and 10 HD Streams was also used Watchout. Women on the Verge of a Nervous breakdown uses Watchout, the off-broadway show Spirit Control used Watchout. All of this stuff is from 2010.
Other solutions exist, for example American Idiot uses Green Hippo Hippotizer, and Fela! uses the uva d3 system, but Watchout is a large and current presence in professional theatre. The case is certainly not that “they all use media servers now.”
One final note on Qlab. Qlab is not a great solution yet. It is fine for small productions with tight budget limits, but it is not ready for video on a large scale. For audio, there are plenty of Broadway shows that rely on Qlab. One interesting thing that people do with Qlab for video is use one computer as the cue stack, and send MIDI commands to additional computers running Qlab that playback video, one for each video source, sort of like a manually pieced together Watchout system.
Daniel Brodie
https://brodiegraphics.com