If you are judging the shape of the teams by the games in the League of Nations, then most likely in vain. Firstly, no one takes them seriously (except for outsiders and teams that are left out of the main tournament like Italy). Secondly, even if these teams are not in shape now, what difference does it make? After all, it will only matter how fit they will be during the World Cup, which does not start tomorrow. In terms of climate conditions, hasn't Qatar guaranteed that there will be some kind of super stadiums with fully air-conditioned throughout the stadium? I think I've heard something similar.
If teams from any continent have an advantage at the World Cup in Qatar, it is clearly not because of climatic conditions. I think that the organizers of the tournament will fulfill their promises and solve the issue of a comfortable temperature at football matches, especially since FIFA specifically decided to hold the tournament not at the usual time, but in another period precisely because of the temperature factor, when the temperature will no longer be so sizzling. As for the significance or non-significance for the top European teams of such a tournament as the UEFA Nations League, I would like to say the following that neither a single national team nor the players themselves will bring themselves to the peak of their physical form right now and will just try to do it a little later when the World Cup is held.