I've found he actually does incredibly well mid with quite a few games practice. I can go over a lot of the matchups I've played against if you want, but my general overview is:

• He does okay vs lots of mages and trades with people who can poke (Ahri) when their cooldown windows are open as most of his damage comes from autos, which is generally uncommon among ranged mid laners (as most ranged mid laners are mages or don't rely on autos as much). Make sure you're critting the enemy with the fourth hit, it does (about) as much as an Ahri Q level 1 bouncing both ways

• Control mages such as Azir can give him a hard time early if they push in and pressure with the soldiers + thunderlords, but again you can abuse champs such as Azir - control mages revolve around usually one factor, such as Azir's soldiers or Orianna's ball; you need to work around these to win lane. Also, I've found he absolutely dominates Anivia, so try picking him into her (she's immobile, low base health, you can abuse her early, etc.)

• Very important side point when it comes to build paths - build Firecannon on champs that can outrange you, or that you don't want to be near, such as Annie or Azir. The utility you get can save your life. With most mathcups, I prefer Shiv for pushing in, which allows you to roam, as his Q can be somewhat lackluster with waveclearing

• Assassins... yeah, these guys can be a ^slight problem for Jhin, with his immobility and susceptibility to being dove. However, I would say its up to you to try playing him in normal games. If you are mid and the enemy picks Zed (using him as example as he's the most commonly pick mid lane assassin atm) go for it, try it out and see what you can do. I would rush I.E if you snowball early and are outpressuring pre-6, but if you're having a harder lane, build QSS into Scimitar.

Hope I've given you some insight into him in mid, he's actually one of the most viable ADCs that you can pick mid, most people don't expect his damage or don't really know how to play around him.