>[heatpump waterheaters are] WAY more complex to plan, install

Only if you place them within <700sqft (for a typical indoor residential location). Only in areas smaller will you need to duct them, somewhat similarly to:

<https://i.imgur.com/4wCez9u.jpeg> this specific design draws from both bath and bedroom [dual 6" inlets], exhausts into kitchen [single 8" outlet] | utility closet is only 5ft x 4ft (~20sqft)

As an added bonus it'll passively dehumidify/cool whereever it drafts to/from.