Even the criteria you somewhat arbitrarily select are not particularly sound. You may have overlooked the doubtless uncomfortable (for you) facts that the Union began when a Scottish monarch (James Sixth and First)was invited to take over the English throne; and that the present constitutional arrangements in Northern Ireland were endorsed in a referendum by the people of the island of Ireland as a whole, both the North and the Republic.
Yes, and natives sold Manhattan for $24; the deals those people made died with them.
I don’t think the native Irish in the north put much stock in what southerners (who did win their independence) signed away for their northern kinsmen); a civil war was fought in Ireland over the question, so I don’t think the betrayal of the north was very popular. Ireland will get its six counties because of their birthrate; England clung to the industry in the north, but that died decades ago - it is now an economic albatross around their necks.