That's pretty much it. I'm studying WWII on History class, and I keep reading stuff like "the Russians occupied Berlin" or "Latvia, Lithuania and Estonia were Russian Republics". Shouldn't they be called Soviets? Russia was just one of the republics that constituted the Soviet Union...
The same goes to the UK. I keep reading stuff like "France and England landed on Normandy on D-Day". It wasn't just England, it was the whole UK: England, Scotland, Wales and Northern Ireland. They also refer as "English" to citizens or soldiers from the UK... and it's really uncomfortable.
What really sticks out is that a lot of very good sources use this terminology: Oxford and Cambridge academic books, IB books, BBC, CNN, National Geographic... etc.
Is it like a standard among historians to accept those kinds of generalizations? What's going on?
I don't think it's used so much by historians anymore, but I do recall reading that it was quite common to say, e.g., England to refer to Britain prior to WWI - and possibly afterwards too. I think it's basically a form of 'metonym' - using a word commonly associated with something instead of the word itself. Like how people say Washington or the Kremlin nowadays to refer to the countries' governments.