Alice, it is spelled Barry Lyndon (even though it sounds like Barry Linden). Sorry, I couldn't resist.

I think we always need to take it with a grain of salt when we hear that non-solo playing did not exist before a certain date. One can say that solo playing was the norm for performance events and dances, etc. But absence of evidence is not evidence of absence; the people who wrote about music in pre-famine ireland (tourists, for the most part) would not have been invited to events of purely social music-making. So we have accounts of weddings, wakes, dances, saint's day celebrations, and other public events, but few accounts of what went on in the kitchen.

One thing that would tend to contradict Hammy Hamilton is that as soon as recordings appear in the US, in England AND in Ireland, ensembles are there to record. The ensemble may have become more popular because of recordings but it is probably not a wholesale creation of recording technology. This is the same with American old-time music; string bands did exist and sometimes sang ballads with accompaniment, but it was the advent of recordings that cemented the ballad singer with his banjo and guitar accompaniment as the norm.

So anyway, I suppose this is thread drift since we all know the guitar was rare in Irish music until recently. But, as John P says, it's obviously a big part of the culture now, so you can't worry too much about the long term traditionality of the instrument.