Your argument leaves aside the fact that Germany lost the second world war and was absolutely devastated by it, and that a lot of their military power in that war came about at the expense of their citizens. It's also way too narrow: the resources the UK devoted to controlling its empire, couldn't be devoted to holding Germany down. The UK was never the sort of monopolar superpower that the US was 1989-2008 (the US very much learnt from the UK's more primitive form of partial dominance).
Moreover, even if any of your claims are true, it still doesn't show that they collapsed due to domestic politics. If they didn't have a goal of maintaining their global empire - and you seem to argue that they didn't - then it's not domestic politics but rather public opinion that led to the end of the empire. That is to say, it offers no real lessons for a country that wants to remain dominant. Maybe the US wants to leave its empire behind it, but if so you can only learn that if a country wants to leave its empire behind it, then it might succeed. So what? The British example in your presentation doesn't say anything about a country that wants to remain dominant. And it is completely one-sided, failing to account for domestic politics in China, which is in a far far worse situation than the US in terms of being able to gain/retain the (international) support needed for a dominant position.
> Politically, it is “gave up an empire to gain a continent… hang on, why isn’t the continent doing what we say? That must mean they are dictating to us!”
This is chronologically wrong. The British had already lost almost every bit of their empire, and certainly their imperial standing, before they tried to join the EEC. It cannot be maintained by anyone with even a milligram of dedication to the truth that they "gave up an empire to gain a continent". It's true that the price they had to join the EEC was to end the imperial preference, but they were poor, the sick man of Europe, and their ability to conduct internal imperial trade was dependent on the United States. Even their very best colonies in Australia and New Zealand, although still dependent on imperial trade, had turned and saw their future as key allies of the US - not dominions of the British Empire.
So while it might be the case that more lately, some British politicians have sought to build domestic support by lying to their constituents and claiming they "gave up an empire to gain a continent" only to be surprised that it was a partnership, they didn't lose their empire to join the EU/EEC. Your false-quote has resonance in the context of the Brexit debate, but it has no meaning in the original circumstance.