Wales was indeed first on the receiving end of English imperialism - the Ring of Iron...the pseudo-apartheid of the English settlements in Wales - although the semantics seem to be quite slippery. It was Norman imperialism more than anything although my understanding is Longshanks did see himself as a specifically English king.
Before the advent of the Normans, the 'Welsh' and the 'English' seemed to ally with each other as much as fight each other. Happy to be corrected on that, though. If we go really far back, it's been interesting reading Max Adams's 'The First Kingdom' which valiantly attempts to illuminate the British Dark Ages by collating much recent archaeological work to undermine simplistic notions of some sort of post Roman/Arthurian Anglo-Welsh race war.
To get rid of English nastiness, I guess you have to get rid of England itself as the dominant geographical and population centre of the Isles. If the Heptarchy hadn't coalesced into a single English kingdom (which happened unusually early for England as I understand it), then you can imagine a separate 'Northumbria' and 'England' (Wessex-Mercia) so that the 'Anglo-Celtic' equation might be a little more balanced rather than being so lopsided in England's favour.
More recently, if you butterfly away a lot of English nastiness (and God knows, there's been plenty), I guess Scotland, Ireland and Wales become quite different places in that elements of their national identity are defined in terms of resistance to the English. Then again, elements of English identity seem to be based on the same kind of psychology (anti-French, anti-continental...etc etc), so they're hardly unique in that.
And now I've just read the rules of the OP properly, so ignore most of that. Sorry!