Not only is it per tick, but it's also scaling upwards by 33% against an individual target. The % itself might not sound like much, but let's talk actual numbers here, shall we?
Let's say that you are Garen with 100 bonus AD. What's the difference between a rank 1 Judgment at level 1 and a rank 5 Judgment at level 9?
At level 1, you deal 46 damage 5 times, which is 230. Against a single target, that number increases to 306.
At level 9, you deal 50 damage 7 times, which is 350. Against a single target, that number increases to 465.
So, as you can see, there are lots of different intricate bonuses going on here besides the % bonus AD ratio. But even though the two Garens above had the exact same AD, the difference in rank made a huge difference.