Matches in this league mean absolutely nothing. Recently, for example, the Netherlands won 4-1 against Belgium. Do you really think it will be the same at the World Cup? That game could also have ended in 1-8. At the World Cup you see a completely different team. As mentioned before, many players but also coaches consider these matches as practice matches. The only thing is that it counts for the FIFA ranking, in which points can be earned. Those matches are played when the competition is already over, nobody wants that of course. And the risk of injury is also quite high because of that.
They don't mean absolutely nothing, it's still a humiliating defeat though. It just doesn't mean the same as if it was in the World Cup.
I would say a Nations League match is worth about 5% of a World Cup match in terms of what it means in the minds of the players and the public in general.
Agree with what you said, due to the fact that not many serious teams are here because they obviously want to measure how their preparation starts from tactics and everything related to performance they are also clearly good observers for other teams and the league of nations is depending on the strategy whether they want to show their original performance or just to test because in this case many teams are not serious and even just do a few player rotations to test players.