I did a similar presentation a couple of years ago.
Actually the first "MCC" as we know it was indeed the Westinghouse 11-300, but was not an MCC per se until 1950. Prior to that what they and all of the other motor control manufacturers did, was to mount individual combination starters together in a modular "rack" like system with bussed gutters, to which you hard wired each starter. This is what Eaton refers to in their history timeline (likely what you read) that goes back to 1935.
Almost everyone else called these "Modular Control Centers", Westinghouse called theirs a "Motor Control Center" and introduced the concept of plugging their 11-200 motor starters into a horizontal bus duct instead of hard wiring (because, of course, they made plug-in bus duct too). But that wasn't really the 11-300 yet. What changed was that in 1950, they released the new version of their Motor Control Center, the 11-300, which had VERTICAL bus bars and the ability to plug in the starters in VERTICAL sections like we do now. It was a response to the "Big 3" automotive mfrs demanding a change. In the post war boom when everyone was buying cars as fast as they could make them, the auto mfrs had to start BUILDING the next model production line while the EXISTING line was still in operation, then it was only good for a few years before they were forced to make wholesale changes again. So they wanted a way to allow their electricians to re-use and reconfigure motor controls from a previous production line without having to engage their high paid ivory tower engineers. The plug-in MCC concept provided that, along with the concept of NEMA rated motor starter sizes that could be adapted by simply changing heater elements for a number of motor sizes.
The Big 3 liked it so much, that almost all other motor control suppliers followed suit within a few years. You will find that some of them came out with their initial MCC offerings in the mid 1950s, more in the 60s and the stragglers, like A-B and Sq. D, in the 1970s after waiting until there was an actual UL and NEMA design spec established, which took almost 2 decades from the initial concept.
Here's the rundown as I know it:
Siemens = ITE, Rundell, Gould, Allis Chalmers / Louis Allis / Siemens Allis, and Furnas
Eaton = Westinghouse, Cutler Hammer, Klockner Moeller (North american stds.) and indirectly via Challenger; Federal Pacific / Sylvania,
Schneider = Square D and Telemecanique (also Gould overlap)
Rockwell Automation = only Allen Bradley
GE = GE and Bulldog (Trumbull)
ABB = ABB (new to North American stds); BBC (Brown Boveri Corp, which is part of what is now ABB) was brand labeled Furnas MCCs so ABB is not connected.
