Re point 4 the real reason is that the English have never remotely come close to facing up to their history of oppressing and subjugating the Welsh, and (unlike the Irish) the absence of any meaningful diaspora means it generally goes unnoticed that this people, the original inhabitants of Great Britain, the original Brits, were stripped of their power, language and dignity, renamed "foreigners" (the etymology of "Welsh", whereas Wales means "land of foreigners") in their own land, and lost all powers so that essentially they were an appendage of England (a principality, not a country, and one without a recognized capital city until 1955), that power having been gained by intense military force, as the long line of very impressive castles along the border might well indicate. And then much later on industrialisation despoiled substantial parts of the country (which served to benefit not the Welsh so much as immigrant workers from Scotland, Ireland and Northern England), and then deindustrialization added to the despoilment...

I am not Welsh and have no Welsh ancestry (whereas i do have those connections with England, Scotland and Northern Ireland), but quite honestly if one people have the right to hate the English and demand reparations of them (the slave-trading states of West Africa certainly have no such legitimate claim and really need to be told to stop taking the piss), it is our western neighbours. When I was at school in England in the 80s/90s, they were the one ethnic group it was fine to mock. And I don't even know if it's true about the sheep