Garry Lager – agree with your assessment of Luke Kelly. Grew up listening to a lot of him with The Dubliner's but then got into T Rex / Bowie and then Punk. After hearing The Pogues in mid 80's went back through Christy Moore to listening to Luke again who died tragically young.
Recently stumbled across his version of a Town I Loved So Well, beautifully sung, of a song I had sort of dismissed
Luke is peerless tbh, no one comes close. That song you mention is a great example of something that would sound a bit corny being sung by a lesser voice, but he's that good he always transcends the sentimentality.
Another one is 'scorn not his simplicity', written by the same guy (Phil Coulter). Potential for a disastrous mawk-fest here, but Luke Kelly just puts it over the top – heartbreaking song.
Saying that, there's a lot of Dubliners stuff that has to be sung by Ronnie Drew. Not a world class voice, at all, like Luke, but can be just as powerful in its own way.