Well, that is merely a difference in character's internal motivation. This indeed will make character's feel rather different, but it is a rather bizarre justification for a massive mechanical difference. It is not like we have completely separate class with different mechanics to represent a selfish thief who only steals to enrich themselves and one who does so to give it to the poor.
The Cleric gets a wide range of powers and spells that come from opening themselves and cooperating with the divine. That feels like Wisdom based to me.They get to directly channel positive energy as a conduit for their (much more senior) partner.
The Warlock is exploring the arcane (or would maybe take anything that came their way), and stumbles across the otherworldly bargain to gain that power. I can almost imagine any of Intelligence, Wisdom, or Charisma here, but the latter two and needing either willpower or sense of self to not just become a puppet seems to fit for me. If I were going to merge the warlock with something I think I'd go Sorcerer before Cleric (instead of your blood, you get the power from the bargain).