I think it was a sensible decision to drop their own engine as nobody liked it anyway. Might as well go with a proven one and use your resources on stuff your customers want you to focus on. Since Nadella took over, Microsoft has been very well managed imo and they made a lot of right moves, like their move into cloud computing, embracing open source, integrating linux subsystem on windows, etc…
Their choice to ditch their IE/edge engine is a symptom of these better managerial choices.