Harpoon missiles are being used in a land attack role.
If the target is valuable enough to warrant the use of a costly missile like that then so be it. Weapons that are too precious to use are by definition useless.
You’re right. There aren’t too many significant targets left afloat for the Harpoons in the Russian Black Sea Fleet. The ones that survive are either submarines or sheltering in Sevastopol under land based SAM systems. A huge waste of money and manpower.
So Ukraine may as well make use of the Harpoons since the Russian Fleet isn’t going to leave harbor to make sure they survive.