this is the question I have always asked about the supposed 'labor savings' of new technologies and system, and never got a sufficient answer to: what exactly are these wonderful 'other things' that we could be doing?
You have a wonderful array of 'perhaps'es here...and for each positive one you put up, I'm sure I or someone can come up with counterexamples that are not positive...
So, let's just say instead of one single AI we have any array of them, checks and balances as it were, as you suggest. What if they decide to form alliances and go to war for control...with humans as expendable or merely inconvenient collateral.
Or, they decide that it's stupid to serve humans, and unite to form a dictatorship, denying humans any and/or everything that we might want, push us off onto reservations, sterilize us, and let us die off quietly.
Maybe they'll keep a few of us around to be entertaining servants...