I suppose I'll weigh in here since Aliana and I have been back and forth on this topic a bit already.
It seems that, at level 30, favored soul builds are objectively optimal for the holy warrior archetype. A cleric/hospitaler provides access to more features in the mid-levels, and remains strong, but the stat spread is less favorable.
Compared to either of these options, paladin suffers for all the reasons mentioned above. I considered paladin when I made Arilyn, but opted against it because there are simply better ways to build a holy warrior, and I wasn't interested in the class for its own sake.
This strikes me as true. And you're forced, due to multi-classing restrictions, to stick it out or pair the class with something that doesn't offer it a whole lot. So the rules are at odds with mechanical proficiency.
The niche for a paladin vs. a cleric (or a cleric analog like favored soul) is that former focuses on melee while the latter are more proficient spellcasters. The existence of hospitaler and the ease with which you can build a strong melee cleric or favored soul significantly muddy the waters.
So, any buff to paladin should probably amplify its proficiency in melee vs. the cleric types, and also reward a deeper level investment. A good place to start might be to look at substantially buffing the Holy Sword spell, and making its bonuses scale powerfully into the epic levels - it has more of a niche on low magic servers but given the spell changes and loot table here, not so much. Thematically, this is about as pure a change as can be made. Could also look at adding some unique-to-paladin spells that also scale favorably with a deep investment in the class.
That would make a player like me, who chooses a general archetype and then strives to optimize it, take a second look. Some extra feats? Not so much.