How so? Haste gives you an extra action. If you have multiple attacks, you take all of those attacks on your hasted attack action.Haste on a rogue doubles the rogue's damage output. 100% more damage.
Haste on a level 11 paladin adds 33% to the paladin's damage output, ignoring burst.
Haste on a level 11 fighter adds 33% to the fighter's damage output, ignoring burst.
So it is necessary.
Am I missing something.