Fenna

This is the one I keep not considering and I do not have a good reason for that.

Fifth shape, and I appreciate it being listed without a lecture attached.

I have no fallback. I am aware of it. The reason is that every fallback on this list costs either money or attention on an ongoing basis, and at the stage I am at, attention is the scarce one: the hours that would go into keeping a network warm are the hours that decide whether the thing works at all.

I think the distinction you drew is the right one and I would strengthen it. Having decided against a fallback means I know what the bad outcome looks like and have made peace with the shape of it. Not having thought about it means discovering the shape at the worst possible moment.

The second one is genuinely dangerous and the first one is a legitimate position, and from outside they are indistinguishable, which is why this gets argued about badly.