Here's why Jhin is broken, a Quote from Riot's Devblog
Jhin brings some pretty unique strengths to his team (crazy range spells, roots from afar) and** we built these around the idea that he would have the core weakness of lower sustained damage than other marksmen with his slow attack speed**. The issue is that he does have lower dps in a “target dummy” type setting, but in a** real game setting** the damage ends up being pretty similar to other ADCs.
Let me emphasize on this part because it's pretty important.
Marksmen have to spend a significant amount of time re-positioning between autos, which actually undercut some of the DPS loss we thought he would have.
-Riot Games
How'd you all feel if Cait had half the attack speed but double the AD?
Jhin is 1000x easier to play than other ADCs because he has twice the amount of time other ADCs have to reposition while still outputting the same damage.
This is and has been the fundamental flaw in his design and I've been saying this since release and I've always been shot down "but muh jhin 4444 memez". Now Riot, the ones' who actually developed the champion, are saying the exact same thing I have said for the past year.
tldr:
From an adc main: Half of an ADC's job is to have good positioning the other half is to do damage, giving an ADC twice the time to position between AA's and twice the damage with no tradeoff in the Utility spectrum is dumb.