I don't think this is an admission that Edge's engine was inferior, just that it might be easier to convince people to use Edge if it used the same engine as Chrome. Using Chromium is just one less reason to not use Edge.

I mean if Microsoft can somehow shed the "Windows 10 spies on me" sentiment echoed so much around these parts then they might be able to capture some market share from Google who is more and more being perceived as big brother spying on you.

I doubt this move will help them but it will definitely make the justification for Enterprise adoption of Chrome a little harder.