Essentially, I was saying the the one-to-many, centralised way of handling plenaries usually sucks because it's very hard for one person to genuinely engage the attention of a diverse group of people.
I wanted to add one contrasting point, which is that there have been some occasion where a plenary with multiple voices has worked. And when it does work, it can work remarkably. It does require a different kind of commitment and attention from participants and a quality from speakers that I summarise a bit simplistically as authenticity. When this happens, there can be a very powerful sense of connection and a sort of dialogue we rarely manage in organisations. My sense is that this tends to happen when it's very clear from the invitation that this is the intention - but that doesn't always guarantee it nor is it always necessary.
The mantra that "nothing is written" is somewhere close to the heart of my way of working, and I just wanted to add this qualification to what I said before.