Suspending someone in SOME situations is better (If you have another team member to follow up), on the other hand a silence is better 1v1, because while you are holding the enemy in the air, you are holding yourself in the air as well.
And no its 150% bonus AD, that would be over powered as shit if it was 150% total AD.
Also Yasuo can knock them up by himself, but he needs two stacks of Q's, he can't just ult whenever, or if a team member knocks them up, they still have A LOT longer to prepare. Since you know you can only be ult;d if you get knocked up
"ACTIVE: Yasuo blinks to the nearest visible Airborne icon airborne enemy champion to the cursor, instantly generating maximum Flow. Upon arriving, he Stun icon suspends all nearby Airborne icon airborne enemies for 1 second and deals them physical damage.
PHYSICAL DAMAGE: 200 / 300 / 400 (+ 150% bonus AD)
For the next 15 seconds, Yasuo ignores 50% of his targets' bonus armor. Casting Last Breath clears all stacks of Gathering Storm."