Taking one of my prior suggestions from another thread, how about having Henry II gaining the approval of either Pope Alexander III or his successor to have John crowned King of Ireland? From that POD, John Angevin's first visit to Ireland in 1185 goes far better than it did IOTL, and John I is successfully coronated as the first King of Ireland, with him and his successors going on to develop and expand the Irish economy, increasing the efficacy of Irish taxation and established numerous new Irish market towns. In contrast, in this TL, the English economy largely stagnates relative to that of Ireland- John never becomes King of England, butterflying Liverpool (a town which he personally founded by royal charter himself in the early 13th century) out of existence, with far-reaching consequences for English colonial aspirations.
Due to butterflies, John's elder brother Geoffrey escapes his death in the jousting tournament in 1186, becoming King of England instead; Geoffrey's personal friendship with Philip II of France sees Geoffrey retain his place as the ruler of Normandy, Brittany and Anjou, as a vassal of Philip II; the long-proposed marriage of his daughter, Eleanor, to Philip's son and eventual successor, Louis VIII, goes ahead without King Richard alive to interfere, and the Angevin kingdoms on the mainland soon merge with the Kingdom of France. However, he becomes a far more neglectful and tyrannical ruler in England than John I ever was IOTL, rousing far more resentment about his even worse misgovernment, fiscal policies and treatment of many of England's most powerful nobles.
As such, with the Magna Carta never signed ITTL, the First Baron's War becomes a full-blown civil war, one which ousts the Angevin dynasty permanently. Largely indifferent about the loss of England, with his primary focus on France, Geoffrey withdraws from England; and the Kingdom of England fragments, with the 25 (probably more ITTL) feudal baronies fighting against one another for dominance, and England becoming a patchwork quilt of principalities with no true king, to an even greater extent than Germany and the contemporary Holy Roman Empire.
Because of this, the primary base of power, wealth and trade in the British Isles shifts permanently from the chaotic, divided and war-ravaged lands of England to the stable, unified and well-governed Kingdom of Ireland- with Llywelyn the Great, one of John I's greatest allies and son-in-law IOTL, and the Kingdoms of Wales under his dominion, eventually becoming vassals of the Irish crown instead of the English crown ITTL. And following the marriage of Alexander III of Scotland and King John's grandaughter Margaret, the Kingdoms of Scotland and Ireland are subsequently unified under the rule of their only son and heir to both thrones (following the death of Edward I in the Ninth Crusade, with the Muslim assassin who stabbed him with a poisoned dagger in June 1272 successfully killing him).
Would you say that this would satisfy the requirements of this thread?