Well you’re wrong. Winning countries, yes, sort of, except neither France nor China could really be called that and UK did little more that survive. When the U.N. was being set-up France, USSR and UK represented empires which no longer exist (in fact France and UK’s were already falling part).
So, the population component that they represented has fallen away. USSR population also halved when its seat morphed into just Russia.
That might be your view, but you are in the minority when it comes to the Leave camp as a whole. “Spend the money on us!”. “Why should people like this [photo of miners from early 80s] have to work until they are 70 to support people like these [photo of Syrian refugees]”. “Send them back and give their council houses to hard working Brits!”.
Just a sample of messages I see every day on social media … and I’m not even signed up to any of the far-right Brexiteer ‘time to take back our empire’ fake news sites, but some of the people I grew up with obviously are and this is the type of things they often ‘share’.