Just curious, how do those numbers compare at 8th level, no feats?
I've seen multiple paladins, but our highest-level character is just 12th (and the BM is only 7th), and I don't allow feats. In those middle levels (5-10), the paladins seem to have a far greater ability to nova than a fighter. A fighter (or barbarian) is more consistent across multiple fights, but for the BBEG, the paladin is hard to equal.
For a valid comparison you'll need to compare across all levels and average out the DPR, with more of a weight towards level 3-10 where most campaigns in reality actually play out.
OK, extra damage gained from Divine Smite (all hits, maximum available slots) vs. Action Surge + 2 on-hit Superiority Dice. Again, greatswords for both Paladin and Fighter w/ GWF Style. GWM's -5/+10 trade for Fighters in parentheses after:
Lv. 3 (STR 16 for both characters)
Paladin (Divine Smite): 2d8 = 9
Fighter (AS+2SD): 2d6r1&2 + 3 + 2d8 = 20.33 (+10 if -5/+10 trade)
Lv. 5 (STR 18 for both characters)
Paladin (Divine Smite): 3d8 + 3d8 = 27
Fighter (AS+2SD): 2*(2d6r1&2 + 4) + 2d8 = 33.66 (+20 if -5/+10 trade)
Lv. 8 (STR 20 for both characters)
Paladin (Divine Smite): 3d8 + 3d8 = 27
Fighter (AS+2SD): 2*(2d6r1&2 + 5) + 2d8 = 35.66 (+20 if -5/+10 trade)
Lv. 10
Paladin (Divine Smite): 4d8 + 4d8 = 36
Fighter (AS+2SD): 2*(2d6r1&2 + 5) + 2d10 = 37.66 (+20 if -5/+10 trade)
Lv. 13
Paladin (Divine Smite): 5d8 + 4d8 = 40.5
Fighter (AS+2SD): 3*(2d6r1&2 + 5) + 2d10 = 51 (+30 if -5/+10 trade)
So as you can see, the Fighter (at least the Battle Master, anyway) consistently novas more strongly through levels, even with the Paladin Smiting on every hit. The Paladin CAN stack a Smite spell of some sort on one of those hits to close the gap in some cases, but only at Lv. 10 would that actually pull the Paladin's nova ahead (without GWM's trade). And the Fighter would jump right back in front of that with its 3rd attack at Lv. 11.
Also Paladins can use GWM for -5/+10 as well quite easily don't forget, and their damage output also means they're very likely killing creatures and procing that extra attack.
Sure, but the -5/+10 part of that feat doesn't affect Divine Smite directly, whereas it does benefit Action Surge directly.