I don't think "phasing out" Symbian earlier would habe been better.
I thought it was quite a good strategy to develop on Qt for Symbian as well as Maemo/Meego.
I am not an app developer, but from what I understand it would have made transition form Symbian to Meego quite easy.
At that time there wer many (many many...) more Symbian developers than Android developers.

More important:
The reason for Nokia failing was not that they were not able to technically compete with the stripped-down and restricted iPhone OS, let alone ugly-as-hell and buggy Android of that time.

There was a series of terribly stupid management decisions (like ditching advanced and touch- optimised S90 and UIQ to go for much simpler S60) leading to first problems until Elop came and deliberately killed Meego and Symbian (I can't beleive he was so stupid not to see that this was what he was doing with hist "burning platform memo", Delaying release of N9 and N8 and releasing N7 on the very day he announced that Nokia would be going Windows-only from that day on).

Some points in that article seem to completely overestimate iOS' and Android's capabilities in their first years of existance.

Apple was great at marketing, and Android was a niche product until Nokia killed Symbian and its designated successor so millions of people switched from Nokia to Android phones.