You are obviously going to the wrong places Johnny. Not all traditional music venues rely on "diddly diddly" music although if the session is predominantly Irish then I'm afraid thats the fashion these days

As regards etiquette ........ a well run folk club will always ensure that singers/musicians get proper order and is worth patronising even if you have to travel some distance to get too it.

As for your hankering for the past ... there have been many similar threads but no definitive answer .... young/new enthusiasts will always interpret a tune or a song in their own way and life would soon become boring if there were no variations