Meego was "already working" (with scare quotes.) Maemo was great, and shipping. People used it and enjoyed it. It had an extremely lively developer community, and the cheat that since it was based in Debian, new apps could be written as UIs added to common, standard commandline applications. The scare quotes are because the relaunch as Meego was pointless, but was also working well enough.

Windows phone was not going to work because the brand is herpes, and Microsoft makes technical decisions based on business strategy rather than merit (and everybody know it.) It had nothing to do with the amount of resources put into it, which I'm sure were vast; Microsoft is happy to lose money in markets for a decade or two in order to block new entrants, waiting for the market leader to make a mistake. If people wanted a phone that would trap them into a rent-seeking ecosystem, they already had a choice in iPhones that was at least attractive and common.

Meego phones could have slotted into the nerd/serious phone category that various Android distributions have awkwardly tried to fit in. It would have also been a non-US alternative for markets like Europe and China. They also could run Android apps within a VM.

I think your last paragraph concedes that Meego could only have gone for a small niche. Nokia had huge market share. There’s no way they would have limited themselves to being a phone for nerds. If they had done Android right, they could be up there in Samsung’s place.