Wikipedias are not merely localized versions of each other, they're truly independent.

If you happen to know two languages and want to quickly rack up edits (if that's your sport), arbitraging knowledge between two Wikipedias is one way to go.

Wikipedia is not throwing their weight around. They are merely pointing out that the law happens to make their operating model illegal, and surely that can't be the intent. If they are illegal, they cannot operate. Is "very well, we disagree, but if you truly insist, we shall obey the law and leave" throwing your weight around?

And yes, I get the impression that the UK's letter of the law could lead to a categorization with rules that (a) Wikipedia simply cannot comply with, and still be a Wikipedia. So in that case Wikipedia would be effectively banned.

But we're not there yet. Hence the use of proper legal channels, including this court case. Ofcom is expected to make their first categorizations this summer, so this is timely.