"a person 'in charge' will make sure that at a tunes session there is an hour or so of each"

This exemplifies what I was talking about earlier. There's nothing at all wrong with Scottish, Irish, Welsh, French or any other music. But a good session is an organic thing, a product of the common purpose of the musicians. If it has a leader, that's by informal, tacit, agreement.

A dozen years ago, at a northern English folk festival, one pub had:

An English (spontaneous) singaround in the "private" room.
A holybejasus Irish session in the bar next door (fortunately sufficiently soundproofed both ways).
A Welsh session in the corridor.
Another Irish session in the other bar.
And an organised folk club upstairs.

And there were other pubs to go to if none of those suited. Pubs aren't like that these days.