The description of guardian of faith (a 4th-level cleric spell) states:
A Large spectral guardian appears and hovers for the duration in an unoccupied space of your choice that you can see within range. [...]
Any creature hostile to you that moves to a space within 10 feet of the guardian for the first time on a turn must succeed on a Dexterity saving throw. The creature takes 20 radiant damage on a failed save, or half as much damage on a successful one. The guardian vanishes when it has dealt a total of 60 damage.
And spirit guardians (a 3rd-level cleric spell), which I will compare to the GoF spell (cast as a 4th-level spell), states:
You call forth spirits to protect you. They flit around you to a distance of 15 feet for the duration. If you are good or neutral, their spectral form appears angelic or fey (your choice). If you are evil, they appear fiendish.
When you cast this spell, you can designate any number of creatures you can see to be unaffected by it. An affected creature’s speed is halved in the area, and when the creature enters the area for the first time on a turn or starts its turn there, it must make a Wisdom saving throw. On a failed save, the creature takes 3d8 radiant damage. On a successful save, the creature takes half as much damage.
The GoF deals 20 damage or 10 if the target succeeds the saving throw and SG deals 4d8 (3d8 + 1d8 for the extra level) and 4d8/2 if the target succeeds the saving throw. Average damage for SG is *(4*8+4)/2 = (32+4)/2 = 36/2 = 18* and 18/2 = 9 average damage if the target succeeds the throw.
Guardian of faith pros:
Damage is higher 20>18 , 10>9
It lasts for 8 hours, while SG lasts 10 minute
Doesn't require concentration, while SG does
Great for long resting in a forest, while SG is for battling an army of goblins
Guardian of faith cons:
Ends after 60 damage dealt, while SG doesn't have a limit
Doesn't move, while SG moves with the caster and also halves enemy's movement
Deals damage when entered the AoE, while SG damages every turn if you stay there
That 1st con makes GoF a lot weaker. If someone chooses to ignore SG it can deal 180 damage!
If I remove the 3rd con will it make GoF overpowered? Will it be too strong, or will it be enough to be a 4th level spell?