We should probably explain when to use this vs confirmationDepth (possibly in a common document referenced by multiple funnels like some kind of new meta category for funnel types in the docs that talks about funnel concepts in general as opposed to concrete funnels)

yeah, but first I guess we may also want to change the carp's funnel config, since now it's different than these (it doesn't have delay).

But it's not really a vs thing I believe. In general I would choose the confirmation parameter and then choose the delay accordingly so that it makes progress without waiting for block production all the time. Technically you can set only a delay, but I'm not sure there is actually a use-case for this.

just a ping that we still need to do something about this

I did some refactoring and added a page for parallel funnels, which now encompasses all of the funnels that synchronize other chains. I think the term is probably generic enough. And also moved a big chunk of the common sections there, including the diagrams. And then I also added some guidelines for the usage of delay and confirmationDepth.