Counter question:
You claim that Clerics feels more Paladin bcs they have deity ...
What difference would there be between Clerics and Paladins, if they would have them aswell?
It's a small difference. I think of it like a Cleric is a believer in their God while a paladin has devoted their whole life to the God. For a real life example. The Christian you see preaching on a street corner would be a Cleric. While the Priest or Nun would be a Paladin.
And that's totally wrong from actual Faerun lore standpoint. A cleric is a person who's so immersed in or important for their god's cause, that the god provides them pretty cool powers. Paladins never reach same divine-magic capability. Real life example would be Moses for Cleric and Paladin for a Nun.
A nun is the female version of a monk.
In the real world monks/nuns are usually followers of a specific religion too.
In my opinion, every char should be able to select a diety, including the choice none.
Back to cleric/paladin.
In DnD both clerics and paladins usually get there power directly from a god.
I think the difference is not their connection to that diety, it´s just if they focus their training more on spell casting (cleric) or more on martial combat (paladin).
Paladins have an oath, but this oath is made to someone. I guess they get trained in a temple (just like clerics) and at the end of their training they: "By ... I swear to follow these tenets" and then they become full paladins.
I say usually clerics and paladins have a diety because their power could also come from another powerful creature.
I was told that the difference to a warlock is that clerics worship this creature while warlocks have a pact with it.
side note: According to PHB paladins chose their oath at lv3.
Prof. Dr. Dr. Mad S. Tist 
