This isn't an academic debate - the rules of logical fallacies don't exactly apply here.

It is about design aesthetics. Having a Start Screen and a start menu is messy and redundant, subjectively speaking.

It is about forward progress. Leaving the Start Menu encourages people to rely on a method they are comfortable with and reject adopting a new direction that may be superior, but unfamiliar and threatening.

It is about efficiency. Certainly having a Start Screen and a Start Menu would consume additional resources on the device at a time when Microsoft is trying to make the platform more efficient and lightweight.

I don't see any false dilemma here.