There are differences, but there are also some similarities. Irish Lugh Lámfada (Long Arm) and Welsh Lleu Llaw Gyffes (Skilful Hand) have similar epithets and Irish Lugh is also Samildánach and Ioldánach (Skilled in Many Arts) as well as being Maicnia (The Young Warrior); this last name is reminiscent of the young Welsh Lleu and his battle to be recognised as a warrior, perhaps. Both figures have unusual births and they are both connected to ideas of triplicity and are seen as skilful masters of the arts. Linguistically, I think there are some serious problems with deriving either Lugh or Lleu one way or the other from Irish or Welsh (as loanwords). Nevertheless, I think there’s a strong likelihood that both characters are descended from an earlier figure, perhaps akin to the Gaulish and Celtiberian Lugus, which might explain the similarities, but also the differences given that we are talking about hundreds of years and a relatively wide geographical distance between them.