"What's the harm in performing a song like someone else if that's the way you personally like it?"

Which is of course what all of us do, when we introduce 'Johnny B. Goode' with Chuck Berry's guitar riff, rather than a moody chord sequence on church organ or a stentorian burst of highland pipes. On the other hand, as a listener I think I'd prefer to hear a singer try and do their own thing with 'Arthur' rather than what is almost inevitably going to be a poor imitation of Paul Brady. The demand here for 'authentic' guitar tunings and tabs rather argues against the idea that an attempted Brady impression is likely to evolve into something new and creatively exciting.

"it may be safe to look for an Ulster source for Brady's version"

The origins of the song in Carrie Grover's Nova Scotia collection has already been discussed in some deatil on this other Arthur McBride thread. Ms Grover claimed English, Scottish, Welsh and Irish ancestry, so it's still quite possible the song had Ulster origins.