What's your guys' opinions on Lee's Resonating Strikes' extra damage?

Is it too weak, too strong, unnoticeable? I just found out that the missing 8% extra damage equals 1 extra damage every 12.5 missing health (compared to Garen's ult being 1 extra damage every 3.5/3/2.5 missing health), which doesn't seem like a lot if done only once or twice in a fight.