OOC Because TTL Revolution gave a more rosy view of the union before it with the problem seen as English domination not a problem with the union itself. Recall that OTL Irish Nationalism has most of its identity forged out of Irish Republicanism, TTL the collapse of the Revolution would discredit most of that, especially if the Revolution comes to be seen as an English thing.
Tbh I grew tired of inevitable UK breakups in DBWIs so came up with a twist. The Confederation is probably looser as you say, and I suspect England was divided at least into North and South territories.
(OOC: Except that Ireland was a very conservative country overall, a communist revolution would if anything only discredit British rule further, not to mention that if Britain was going through a revolution that would the perfect chance for Ireland to break away from Britain with German and Russian help as Ireland would be a valuable strategic base for their navy and air force. Irish nationalism existed before republicanism as can be seen with the Nine Years War/Tyrone's Rebellion and while it became intertwined with republicanism after 1798 it wasn't dependent on it, the leaders of the 1916 Easter Rising considered making Wilhelm II's son Joachim the King of Ireland if Germany won WW1 and Ireland got it's independence, and Michael Collins stated in his book The Path to Freedom that the Irish rejected the British system of government not because it was monarchical but because it was British and that a constitutional monarchy was just as free as a republic.
I understand that but Ireland remaining British in this scenario is simply way too implausible.)
I wouldn't exactly call it a proper dismantlement it just broke English domination and enable the coming Confederation of the British Isles to be representative of all parties, especially our Irish brothers. Not that those idiot English Nationalists see it that way.
Compared to the former British Union or the United Kingdom the Confederation of the British Isles is only a political and economical union than an actual nation, and Ireland is only a member of the customs union part of the confederation rather than a full member in order to maintain trade between Britain and Ireland, they certainly wouldn't consider themselves to be brothers. The English nationalists do have a point when they say that it was a dismantlement.