Voadam
Legend
In D&D I'd say the strongest consistent defining feature is the granting of clerical magic.
I know you are conflating any magic as no practical difference but not all gods can make pacts with warlocks and not all warlock entities can grant cleric magic (Asmodeus as both god and arch-devil in some cosmologies should conceptually be able to to do both). There are things warlocks can do that clerics can not and vice versa even if there is some overlap. That is a practical difference that will be perceptible in world.
It is similar to rangers and paladins, both are magically empowered warriors, but there are practical differences.
I know you are conflating any magic as no practical difference but not all gods can make pacts with warlocks and not all warlock entities can grant cleric magic (Asmodeus as both god and arch-devil in some cosmologies should conceptually be able to to do both). There are things warlocks can do that clerics can not and vice versa even if there is some overlap. That is a practical difference that will be perceptible in world.
It is similar to rangers and paladins, both are magically empowered warriors, but there are practical differences.