I think it was more about economics than competency.
By the end of WW2 the UK was bankrupt and completely ruined economically, while the US had become the industrial powerhouse of the world thanks to abundant resources, manpower, and the fact that the war largely took place far from its borders (a few tiny islands notwithstanding). By the end of WW2 the US owned nearly all the gold that Europe previously owned which led to the US Dollar the worldwide reserve currency.
If the UK wants to pretend that WW2 (or, indeed, WW1) happened like a shock storm, unforseen and unforseeable, with no involvement from them they are welcome to do that. The result of that attitude was that the UK parliament was only allowed to govern a small and increasingly irrelevant island with lousy weather and steadily worsening economic prospects instead of a global empire.
There is a lesson for people governing global empires here - don't allow major wars to blow up on your borders. Or, ideally, anywhere. Maybe spend some time promoting peace and prosperity. Train the diplomats in diplomacy.
You'll notice that the US solution at the end of WWII was completely different to the European settlement at the end of WWI. And the US approach to warring was a lot more staid than the UK's. These are basic matters of competence.
Some fair points, but remember that the US had the benefit of knowing that post-WW1 settlement was a failure. Of course, Wilson did object to the conditions of the Treaty of Versailles, so it's fair to say the US had a better perspective from the start -- though one can argue that the US' own failure to ratify the League of Nations was a contributing factor to WW2.
Another key factor is that the US had no empire to hold together, and, to its credit, wisely did not seek to expand its territory after WW2 in order to create one (which it could have easily done, and which the UK had done many times before).
British weather is great. Enough rain to keep the land green and pleasant, temperatures that don't get too hot nor too cold - the very definition of temperate.
We aren't without our annoying and extreme weather though. Eg in the north of England last week it was -10c for a few nights and a week of 0/1c daytime temperatures with a biting wind chill. Before that was heavy snow and ice.
Heat waves up to 35-38c aren't unheard of. Our houses aren't built for this so a heatwave is quite uncomfortable as houses stay 20-25c overnight
Plenty of flooding in various parts
This autumn and winter has seen a lot of storms
The south fares much better of course and without as much flooding
Nothing important Sudetenland, nothing important in Austria, nothing important in Poland. They tried your strategy in the 30s and it was not a success.
Also, family ties. European monarchs were a really tight bunch. For instance, the tzar of Russia and the king of the British Empire at the time of WWI were brothers.
By the end of WW2 the UK was bankrupt and completely ruined economically, while the US had become the industrial powerhouse of the world thanks to abundant resources, manpower, and the fact that the war largely took place far from its borders (a few tiny islands notwithstanding). By the end of WW2 the US owned nearly all the gold that Europe previously owned which led to the US Dollar the worldwide reserve currency.