It's easy to forget older units in the shuffle of the new hotness, but here's some math. All numbers are on a 100 def enemy.

Cloud Best in Slot, with 75% fire imperil, using Dandelga

• 89,686 base damage

• 493,273 damage using Climhazzard

• 1,883,406 damage using Omnislash (maxed)

2B Best in Slot, no imperil, using Fixed Dice

• 73,536 average base damage
• 734,625 average damage using Self-Destruct
• (Full damage range due to Fixed Dice: 228,974 to 1,240,275)
• 801,542 damage using H0229 Type-B (maxed)

Self-destruct cannot use elements or killers, and does 99% self-damage to 2B, so it's definitely harder to use. Element is already considered in the numbers above, benefiting Cloud; less than a 75% imperil, or using a weaker weapon than Dandelga, and he slides further behind.

While Cloud can use killers, in practice the only type I saw him really beat 2B on was vs humans, since he can use Deathbringer for the free Maneater.

Veritas of the Flame deserves an honorable mention. His Full Charge Stomp is the same modifier as 2B's self-destruct, though his damage is 42% lower than 2B's. He can make this up by imbuing himself with an element and using an imperil. He wins slightly with his baseline 50% imperils, and pulls ahead solidly with a stronger imperil, be it by his own 100% fire imperil counter or via an external source.

I included Limit Break numbers for completeness, though they don't tell the whole story: 2B's LB can chain with a copy, and while it's quick, I think you can weave it into some of the faster chains like Tidus and Onion Knight. I can't find exact frame data for it to confirm. Cloud's limit burst, on the other hand, is extremely long, so you'll only be able to finish with some fraction of it (though the final hit alone still does about 2/3 the damage of 2B's own LB).