I think this discussion may be highlighting a notable difference between customs on either side of "the pond."

For one thing, unaccompanied singing is a proud traditon in Ireland and the UK but almost completely unknown in the US. I engage in a bit of unaccompanied group singing with a bunch of shanty enthusiasts, which itself is pretty rare hereabouts ~ unaccompanied solo vocalization is even more unheard of. The upshot: we Americans don't have singing-only events, and the corollary is that instrumental-only sessions are pretty rare, too, since so many people who play instruments are singing self-accompanyists.

Good singers are musicians, and musicianly instrumentalists should be able to provide sensitive accompaniment to singing. And if a session or jam or whatever is truly going to accomodate a mixture of singers and non-singing pickers, there has to be an agreed-upon plan or "schedule" for alternating sung verses with intrumental breaks.

I think bluegrassers generally know how to cooperate in this manner.

My experience of participating in this kind of group activity, even when things are generally pretty well worked-out, is that the singers (even including those who strum while singing) tend to prefer running through a few quick repetitions and then starting yet another new song, while instrumentalists much prefer to repeat round after round for a much longer time, giving each instrument plenty of opportunity to stretch out and explore the tune, etc.

Finding a happy medium to accommodate both tendencies shouldn't be that difficult, and indeed is not always that difficult, but you have to understand the potential conflict in order to defuse it.