my own take on these claims of descent is utmost sceptism - Gill's Menaw is not the Isle of Man - however it would seem likely to me that in Roman period Mann was more linked to Anglesey than to Ireland, as although the Roman fleet had its northern headquarters on the cumbrian coast within sight of the Island, we see no Roman connection thus I suggest Mann was controlled by a Roman satellite. It is also possible (as I think argued by Broderick) that Mann was bythronic (ie linked to Welsh) rather than Goedelic (linked to Ireland) pre the Norse era (or shortly before)