In my book, Apple had no choice but to do their own map app.
doing their own bundled standalone map app is one thing, inflicting it on the underlying mapping used by the phone and a whole host of third party programs is another.
There are plenty of turn by turn apps available on the app store some with better maps than others. Another one of those, prebaked and included straight out of the box, while leaving google as the underlying mapping for everything else, wouldn't have been a problem.
If they were hell bent on a turn by turn app that wasn't ready for prime time then that's the way they should have went in the meantime.
Ideally with a browser based version that folks could have had a more comfortable time submitting their endless user based corrections thru (and wouldnt have required every business on the planet to go out and buy an iphone just to update their particular location details)