Literally can only do as good as his support. If you get a Thresh or Blitz who cant hook, a Janna or Lulu who can`t disengage, a Morgana or Bard who don`t snare, a Braum who doesn`t hit his slow or any other support who doesn`t do his basic abilities, you are literally Free Food for the enemy lane and/or jungler.
He can`t do ANYTHING on his own. Playing him Mid lane is basically feeding Africa marathon because any champion who has a basic dash/engage deals so much damage to you in such short time, that you can`t even finish to fire off your second bullet and you are defenseless. Even if you snare them, Jhin has such slow abilities/attacks that Usain Bolt will outrun Rammus with full movemend speed build before you are finish casting anything. Any champ , literally ANY champ, outperforms Jhin after level 2.
Keystone masteries on Jhin basically FORCE you to go into close combat, which is devastating and basically suicide, because Warlord`s doesn`t proc on minions, only on champs. Have fun trying to Crit against ANYONE with an IQ over 10 without getting instantCCed into oblivion on your attempt to get some hp back. Jhin can`t afford to build early lifesteal except maybe a quick Blade of the Ruined King, which wastes a lot of potential for the build he is forced into. Full crit. Thunderlord´s works if you manage to keep up constant attacks on champs. But who am I kidding, Leblanc or Lucian are just gonna Dash in on you and nuke down more health from you than a Teemo shroom on Lulu´s ulti.
Any other mastery is basically junk or offers 0 utility for Jhin.
My point is that Jhin is really really underperforming ( GET IT!?) on his own. He is a champ that needs constant babysit and has no chance to do anything on his own without risking making the next teamfight a 40 second 4 vs 5.
He really, really needs some finetuning on his own stats to atleast be able to safe farm for 3 seconds without fearing to die due to the 500 things he has to pay attention to at the same time.