> I would call ensuring the survival of the platform they want to market as "advancing ... Mozilla's purpose".
Mozilla's purpose is to advance the open web. Firefox OS is a means to that end, promoting a platform with that name independent of its actual nature is not an end to itself.
> To ensure the survival of that platform, they're going to need a pragmatic alternative to the HTML5/JS APIs.
The entire premise of Firefox OS, and the only reason that offering it is consistent with Mozilla's organizational purpose, is that Mozilla believes that this is false.
> Perhaps they'll be successful on low-end hardware where applications and games don't matter,
That would be, IMO, a very big success in advancing Mozilla's mission, though probably less than they hope Firefox OS can provide.
> This "all web" viewpoint you seem to be sold on is not sufficiently pragmatic.
I'm not "sold" on it; I suspect that Firefox OS may well be premature. But that doesn't stop me from recognizing that a conventional mobile OS of the type you suggest Firefox should be, with native development along with web technologies, is completely useless for the purpose for which Mozilla exists.
> The right tool for the right job. And non-native SDKs are not yet the right tool for every job.
So? Firefox OS doesn't have to be suitable for every job for it to survive, or for it to advance Mozilla's purposes.