Indeed, Historical Monarchs mode only really works if you not only play a major nation, but actively try and behave as that nation historically did. It's fine as long as you're trying to recreate history, but as soon as the setting significantly diverges from what actually happened IRL (which seldom takes long) it loses all context and eventually breaks down. A bit like getting the Marian Reforms in RTW even if Rome is a weakling one-province protectorate of the mighty Gallic Empire or whatever. The whole time-warping thing is particularly odd.

FWIW the monarch lists for the Irish factions are pretty bizarre and off-the-wall anyway, not one of EU3's most accurately modelled regions.

Antagonist