What if Wales united like the others?

Wales was mostly united under Hywel Dda, but when he died it was split again, Maredudd ap Owain, the same , Gruffudd ap Llywelyn who united all of Wales and others but because of Welsh laws, when they died the kingdoms would be split again .
Meanwhile in England and Scotland, much bigger countries with less in common with each other united and stayed that way .
In Wales, they shared the language, culture, traditions and laws, the Welsh had more to unite them than Scotland and England,
Welsh law said

Cymry – the modern Welsh for all of the Welsh people – apparently only applied to the free classes and not to serfs or slaves. However, none of them counted as a "foreigner" and, even if they moved from one Welsh "kingdom" (gwlad) to another, they did not suffer that status but were considered fully native.

Those from outside Wales were considered between serfs and slaves, forbidden to offer testimony, and obliged to pledge themselves to a native Welshman (even a serf) who would be responsible for them. This status could only be removed after three generations in the north and possibly as many as nine elsewhere, after which the foreigner's descendants were considered to be native serfs.

So do we have Welsh law to blame? If Wales did unite like Scotland and England, would it have changed anything? Would it have been easier for Wales to be conquered, though?

Below is a Map of Wales when it was a kingdom under Gruffudd ap Llywelyn