I have a suspicion that for a task (or to make an artifact) of a given complexity, there is a minimum level of human engagement required to complete it successfully - and that human engagement cannot be substituted for anything else. However, the actual human engagement for a task is not bounded above - efficiency is often less (much less?) than 100%.

So tools (like AI) can move us closer to the 100% efficiency (or indeed further away if they are bad tools!) but there will always be the residual human engagement required - but perhaps moved to different activities (e.g. reviewing instead of writing).

Probably very effective teams/individuals were already close to 100% efficiency, so AI won't make much difference to them.