I agree some of that was true in the past, but I see that unified OS team is a great step, my Lumia 1520 has the same hardware as the Lumia 2520 Tablet, the only difference is the 6" Screen. Most ATOM Tablets are 1280x800, which is approx. the same as most mid-tier Windows Phone, Windows 8.x/RT Apps on WP and vice-versa will be a great addition.WP has suffered from similar issues that BB had, horrible management, incredibly bad market timing, extremely poor marketing and lack of coherent vision, repeatedly deserting the customer base and leaving them hanging with nothing. Its a wonder there's a single digit to the WP market share. Had it not been for some interesting Nokia hardware and Nokia's good reputation WP would be dead and buried. Even now it has one foot in the grave and the other on a banana peal.
Merging the OSs in attempt to save WP may actually kill the tablet too. The last thing tablet users want is an influx of crap phone apps designed for phones and not tablets which to this point has been pretty rate in the Windows RT/Metro space.
And while, Windows Phone isn't huge here, two markets that it has a bigger market share is India and China and in fact in big parts of Europe. The UK Windows Phone Ad Campaign is so much better than here in the US.