The question assumes hat a b bit$b$-bit preimage attack randomly produces b bit preimages. This is not a realistic assumption.
We could imagine a b bit$b$-bit preimage oracle which deterministiclydeterministically produces just a single b bit$b$-bit preimage - never more never less. Running it multiple timeatimes will not give us nothing moreany additional advantage than running it the first time.
Access to a partial preimage oracle does not seem to help at all in solving the full preimage problem.
