I'm just trying to get my head around this. I've read a lot indicating that 'Britons' was used to refer to a general grouping of loose and un-unified tribes, and I've also found that Wales was also composed of loose tribes. So I'm wondering what distinction there would be between them.
There would be no distinction, the term "Welsh" wouldn't be used until Anglo Saxons showed up after Roman evacuation, coming from an old germanic term for "stranger" or "foreigner" The word "Vlach" in Romania has a similar origin, when germanic tribes moved in they began calling natives in the region as such