The Cleric class is weird in the D&D tradition.
Essentially it is a healbot with lots of staying power (defenses, hit points, etcetera) but with weak offensive powers (sub par weapons, sub par spells).
Its only ‘flavor’ is problematic: the baking of a specific multiverse setting into its mechanics.
In other words, the Cleric actually lacks its own character concept, and the setting flavor replaces it.
Aspects of the Cleric traditions that could be useful are:
• gish − full caster with melee combat survivability
• domains − ability to choose a thematic set of spells
• healer − access to healing spells and features as one of the domains
Flavorwise, both the Warlock and Cleric can derive their powers from powerful creatures.
The Warlock makes a ‘bargain’, a pact, to gain powers. This is its distinctive character concept.
Perhaps what could give the Cleric its own character concept is, it gains its powers from a specific spiritual community.
The themes of the specific spiritual community, then determine the spell list.
Potentially, the Cleric is the most ‘linguistic’ character concept. The powers come from the semiotic language of symbols, ideals, and themes.
Ultimately, the character concept is the magical power of words, in the language that a specific spiritual community speaks.
If so, the player needs the freedom to choose from a diversity spiritual communities, or pioneer a new spiritual community, in order to give the player latitude to personalize ones own unique character concept.