The Overton window mainly classifies the kind of ideas that are "politically acceptable" on the stage for which it's defined, using terms ranging from "unthinkable" to "radical" to "popular" to "policy". On the world stage, I would argue that the most left-leaning of European countries define the left end of the window (given that they have enacted left policies), and the most right-leaning countries (e.g. Singapore) define the right end of the window. It's not a matter of proportion.
That said, I agree that the global window is rapidly shifting right, as in your example of France.
Okay, point-by-point:
> Military
I agree that the military does not neatly fit into a spectrum which applies well on the global window of left/right. Reaching instead for political philosophy rather than political practice, I think it's better to introduce the 2-dimensional political compass to understand this rather than relying on the 1-dimensional left/right spectrum: war is more favored by authoritarian politics (which is to say politics that value authority, rather than necessarily repressive regimes, which are totalitarian). I would also say that authoritarianism tends to be more popular on the right, though the Soviet Union offers a clear counter-example. This issue is messy indeed. But, generally speaking, I think that American leftists (as a distinct group from liberals or Democrats) are not in favor of war, whereas everyone right of and including Democrats are generally pro-military and weakly or strongly in favor of American imperialism.
> Social justice
"Social justice" is ill-defined here, and I don't really think Democrats push for it. A positive "social justice", as I understand it, might, for instance, consider reparations, which I don't think any contemporary Democrats have pushed for. Democrats adopt a more equality-oriented (not equity-oriented, which I would argue is more aligned with what "social justice" calls for) approach to social issues, outside of certain matters like ostensible support for affirmative action.
But, I don't think this is the thread to define and argue over whatever "social justice" means. You can send me an email if you want to clear that up.
Is Singapore really among "the most right-leaning countries"?
In 2022, Singapore decriminalised male-male sex. In over 60 countries worldwide it is still a crime, and in over 10 of those it has the death penalty (at least in theory).
While it has been criticised on religious freedom (for banning certain controversial groups such as Jehovah's Witnesses, Hare Krishnas and the Unification Church) – it still is greatly ahead in this area of countries such as Iran or Saudi Arabia. The government is officially neutral between the major religions, and there is no capital punishment for essentially religious offences such as apostasy, blasphemy, or heresy.
Economically, Singapore deviates in a number of ways from right-wing economic orthodoxy – state-owned enterprises play a major role in its economy, close to 80% of its population lives in government-owned public housing, the government runs a universal public health system.