Well, Greg, surely "obvious and clear" must be seen as relative terms, depending on the experience of the accompanist. I inferred from our guest Monahan's query that he may be new to accompanying tunes; and I remember well that, when I first started on the same endeavour, much of the time the harmonic structure was anything but obvious or clear to me.

As far as chordal accompaniment, the piano may go further back than the guitar, but my information is that guitar did not become popular in Irish trad playing until the 1950s/60s. Please correct me if I'm wrong.

Cheers,
Michael