>Did they simply build a deck out of an uniform thickness armour plate, and called it a day, and then this practice evolved to an all-or-nothing design, or is it more complicated?
All-or-Nothing actually predates the heavy deck armor schemes by many years.
That being said, each nation had their own methodology during that times (in fact, this would still be true later) that makes it hard to paint with broad strokes in regards to their schemes.
The Americans, for example, had been trying to run with 3in Armored Decks and 2.5in Weather Decks (main deck), when just having a monolithic 5in Armored Deck (0.5in less metal) would have been far superior.
>And did armoured carriers have similar schemes, or were they different because they focused on defending the flight deck against aircraft?
During WW2, a majority of CVs had armor schemes similar to what you would find on heavy cruisers. Armored Carriers generally added an armored flight deck in addition to this.
>Was it some kind of a design philosophy, or is it simply the result of effectively copypasting their 1910s armour scheme?
>Was it something like that?
The French actually were expecting and planned around long-range engagements with the Italian fleet and were distinctively aware that the Germans were returning to the seas in force, they were however incredibly forward thinking and realized that the proliferation of aircraft combined with their incredible strike range and cycle speed would result in a majority of the attacks against their battleships coming from aircraft. Thus, they armored against what they believed would be the most prevalent threat: bombs.
As it turns out, of course, the French were also incredibly unlucky and the only time one of these hardened turret roofs was struck was from a low angle naval shell at exactly the right angle to draw out the worst aspects of face-hardened armor and would have been the best angle for homogeneous steel.
>Did it became standard in the 1940s for other navies?
No, only the French did that. The Americans purportedly gave a very brief amount of consideration to similar protection schemes for the post-Montana classes, but decided against it.
>And did others skip it because they deemed the protection of non-hardened plates enough due to something to do with the physics of bombs and plunging fire
Effectively, yes. The thick homogeneous plate was the best middle ground protection against all angles of impact, whereas Face Hardened works the best against direct impacts (in the case of decking, from bombs).