Hey, sorry to double post I haven't forgotten about doing Psyduck. Golduck is actually doing very well so far. Psyduck isn't that strong, but you catch him at Level 30ish and that is close to evolution. Sabrina, Blaine, and Giovanni were pretty easy for Golduck. Unlike the listed mid-tier Water types (Seadra/Poliwrath/Tentacruel), Golduck doesn't really struggle against Psychic due to a Usable Physical Attack Stat/no Psychic Weakness.
So far I think Golduck could be better than mid-tier, but maybe the E4 battles will change my mind.