AFAIK they're pretty strong in Pathfinder.
This.
They are the highest tier martial class by most reckoning.
Problem being martial class. An Ordained Champion can get the vital 16 BAB for the 4th attack and still get 18 cleric caster levels, plus a bunch of things related to the War domain. That totally outclasses the Paladin.
Remember also that the original paladin's lay on hands healed a measly 2hp/level which gets completely blown out of the water by a single Heal spell. And that is good old 1st Ed. The disparity becomes worse once things like bonus attacks and weapon specialties (2nd Ed) and more and more spells (3.x) came into play.
That has always been the problem for paladins. They don't stand up mechanically, and I can roleplay the pious chivalric knight with a fighter or cleric. Heck, I can go the Quest for Glory way and play a mage that is a paladin in all but name (Erana). I don't
need to be a paladin.