Personally, I think if the engine was closed source, then we didn't in fact "had that". Maybe Microsoft had it, not us.
What makes things like chromium, firefox and webkit actual ecosystems is that they at least have an open source basis. Edge isn't an ecosystem, it's a black box. We don't even know whether it's true or not that it was its own thing or just they sneakily used bits and pieces of chromium from the start anyway.
User Agent checks is the easiest thing to overcome. Had edge's engine been open source we would have had spins of it resolving the issue within hours. There are many examples of "random developers" succeeding where big companies tied by business strategies (I bet they had business reasons to keep a distinctive user agent) didn't, to the point that the web runs on servers using FOSS software.