When a paladin uses their best limited resources, they should be pretty darn kick butt. All of the classes with depleting resources can do some nice stuff if they deplete their best stuff all at once.
Let's say we have a 20 Strength 9th level paladin with a +2 Greatsword, Great Weapon Fighting and Savage Attacker Feat. He finds himself face to face with a dragon and attacks twice, hitting on both attacks with Divine Smite. He is doing 2d6 + 4d8 + 7 with 1 and 2 rerolled and two damage sets rolled in total for each of the attacks, right? I can see 80 damage there. He is expending two of his most powerful spell slots to do it, and has supporting feats and a great magic weapon, but I can see it.
Now, let's look at a 9th level Sorcerer that throws out a quickened 4th level Ice Storm (2d8 + 4d6 - ~21) and an empowered 5th level Cone of Cold (8d8 twice, use best - ~40). About 60 damage in a large area.
The paladin is focused on one target and does more damage, the sorcerer nails a larger area for about 75% of the damage. Both have blown significant resources. I see no problem... Classes with these types of abilities do very well if they're allowed to take a lot of rests, which means you need to keep them from resting all of the time if you want them to be balanced with the workhorse classes like rogue and fighter that do not deplete resources, but do more when there are no depleting resources being used.
