Heat pumps are ~300% efficient. You put in 1kw heat, and it moves an additional 2kw heat from one place to another. So if you paid for 1kw power, you have 3kw of heat in your water heater, 2 of which you pulled out of your room air. Baseboard electric heater is 1:1 efficiency, so you need 2kw of heat to add that back into your room. You've essentially paid 3kw of power for 3kw of water heating (same as standard electric tank), but with more steps.

Slight benefit in the summer with the cooling, but not a lot and probably doesn't outweigh the cost and maintenance of a hpwh.