Is Summon Elemental Good?
Overall Rating: Blue. This means that summon elemental is a great spell and you should strongly consider this spell for your character.
Overall Notes: Tankier than the fey summon because of the damage resistances but does less damage. Still a great option, just depends on what you're looking for.
Class Specific Ratings for Summon Elemental
The Fathomless warlock: Unfortunately, the water elemental is by far the weakest summon because it has the worst damage resistance and movement buff. That said, it is still effective and scales with higher spell slots.