It was never meant to be a particularly good spell.
What more would you expect from a second level spell that can't be upcast.
The weapon lasts 10 rounds, has decent durability, does a reasonable amount of damage, and has a non-negligible chance to hit.
Additionally, you can cast the spell using a bonus action, and the cleric usually doesn't have many opportunities to use his bonus action.
It's not an insanely OP spell, but I daresay it more than justifies its existence for a second-level spell and definitely serves its purpose.
Maybe poor mobility is one of the ways this spell is balanced. And I won't even argue with you about that.
Flying is useless and overall mobility is terrible too.
