Maybe instead of Cymru (Wales/Welsh is an English(Anglo-Saxon...Waelisc/Wealas) word meaning foreigner/Land of) having to go to Ireland for some "better" units. Which I feel is somewhat wrong.
A) They would be more intested in going East and reclaiming Lloegyr(the Lost Lands, eg: England) back.
B) Ireland in the main was more military backward in it's style of warfare(ok they where learning fast from having to fight the Normans).(This is not said to insult any Irish etc)
C) The Brythoniaid by this time where fighting in allmost the same way as the English, with Knights(or mounted men-at-arms), men-at-arms and of course the bowmen , all had large amounts of the hoi polloi armed with spears/sharpened sticks etc, but with a large amount of raiding/guerilla style warfare added to the mix.
Hence why the English had to build so many castles to protect themselves(and so they could supply themselves from the sea(most are on the coast or on a river estuary).
You Would be hard pressed to see any differance between an English, Welsh or even an (Lowland) Scottish army by now (100 years or so before then yes, you could), only the heraldry (and if you got close enough then of course their language/accents)
So going the other way and into England to reclaim our (I am a Cornishman by blood
) lands back and get units from that roster( eg: Armoured Swordsmen , Fedual Knights(but then can't see why they don't get them (as in the Knights) from the get go, especially as they hold the southern countries of Cymru (like Pembroke..who was the 1st Earl of said place?
and some(or parts of) of the other Marcher Lords lands) etc) whould be fairer than going the wrong way over to Ireland.
Oh dear one does go on abit..and more than likely makes no real sense...but hey-ho thats life.
And while I am going on about about stuff, what about as England has the Templars what about giving the Barons the Hospitallers?. might even things up a bit.