They are not just "merging codebases". They are literally letting it stagnate in all the parts that matter, and all the user-facing parts are iOSified, or literally delegated to iOS with "you can run iOS programs directly now".

And yes. Merging codebases is a bad thing when it's done without any care for one of the paradigms. The one that they don't like, don't understand, and want to go away.