I am German, I live in the UK since 2000 so I think I am fairly good to see both sides.
Not sure why the OP picked Germany, you mean because of the war we shouldn't be a prosperous nation?
Germany has it's issues, it's absolutely not easy and wonderful. Our train system is crap, education has problems, we have unfortunately a far-right party in parliament. In a way the country still is divided even 30+ years after unification because a lot of old problems have never been solved properly and it will take at least one more generation.
But - our set up is different, we are still a manufacturing country plus service, finance so there is more evening out when one sector is having issues.
Our growth for this year is forecast at max 0.5%, hardly something to shout about.
The EU is what helps, there is no issue exporting/importing. Costs can be lower as there are no tariffs or custom, you get movement of workers and that is needed everywhere and I am not just talking about seasonal fruitpicker but proper trained specialists.
What helds Britain back is the mindset of "we are better", "we were the Empire", "we need to be independent".