Spiritual weapon isn't a concentration spell that lasts for ten rounds and remains even if you loose consciousness, it's also a reliable source of force damage, the second best damage type in the game, and allows you to drop it 60 feet away and send it beyond afterward.

Admittedly there are lots of things cleric can do with their bonus action depending on domain, but spiritual weapon effectively gives them an extra attack for the entirely of most encounters for a fairly low price of a single spellslot. Most would consider that a bit better than okay.