> It would have taken much less time to polish their Meego offering.
Doubt it. It took two years to go from the N810 to the N900 and two years to go from the N900 to the N9, if you go on release dates alone. But if you take into account the fact that the N900 and N9 were developed in parallel, you start to see that making any Maemo/MeeGo phone took an unacceptably long time. And even then, the results - while impressive by the standards of open source phones - often faltered by comparison to the rest of the market.
Plus you have to take into account the stated intention of the N9 platform having no future (MeeGo-Harmattan vs. MeeGo), so by sticking with MeeGo, they'd retain zero same-platform advantage, and would probably have run out of cash by the time they'd managed to get sales off the ground.
I'm pretty sure that they'd have a much lower marketshare today if they'd stuck with MeeGo, than jumping to Windows Phone.