Jayce MID is in a terrible state now, and he is unplayable as lower skill champs do more damage
I dont understand why since 9.6 jayce has received so much nerfs, i used to play him a lot, i put in a lot of time in practice tool to achieve doing his combos perfectly, learning all the matchups, flashing abilities from enemies that would make them win the trade with their ignite, to survive low hp myselve this simply is not possible anymore.
if you dont play jayce yourselve dont say he is fine you dont know what ur typing if you truly think he is fine then tell me this if i play jayce in to malzahar right now and play it well, why does malzahar get to press r and kill me losing 1300 gold on a champion that doesnt scale lategame to get a qss doesnt mean i will win the 1v1 against a malzahar who requires way less skill, but then does way more damage to do the malzahar combo's perfectly you just have to press them, to do jayce combo's perfectly you need to be quick forget to press 1 button and ur combo doesnt work.
Also, as jayce you need to aim the q before you place your gate, and then you need to put it quickly near jayce to make it more difficult to dodge if you do the e auto combo in hammer stance you need to spam right click so it goes through if you dont press w in ranged form before you swap you dont get the attackspeed.
Cho gath has a 61.33% winrate against jayce now, a champion jayce is supposed to be a counter to, this is how bad of a state jayce is in right now, its not even tank meta and this tank Cho gath completely anihilates jayce cuz he does no damage early game and if jayce doesnt have early game damage, you cant build a lead so you wont do damage midgame either, then add the fact that you just like zed talon and qiyana have to build lethality to have good damage mid game which doesnt scale, meaning that afther 28 minutes, or 30 minutes when everyone is full build its hell to be jayce at that point, because whatever you build you will do no damage and champions like cho gath right now, the tank is at his prime whilst building hybrid ap-tank in the midlane
Jayce used to be very good in to
veigar, which by the way is a late - midgame scaling champion has a 5.30% winrate over jayce in that matchup simply because as jayce you are not able to outpoke the veigar early game with his q and w level 4 you are not able to win the 1v1 against veigar if both of you start full health EVEN THOUGH you take ignite and the veigar takes teleport
Now lets talk about a what used to be even or skill matchup,
If annie presses ult, stuns you w's you and ignites you you will die because the health nerf to jayce in 9.6 makes it so you will not have enough health to survive that, before 9.6 you could slowly poke her with q'es to 60% health and then all in her with ignite, gaining the Triumph heal so you would survive annie's ignite ult q w combo Now at this very moment Annie has a 10.30% winrate over jayce in that matchup which to me is horrific.
Jayce has gotten Nerfs to his q, which are completely unnecessary as veigar only has to hit 2 or 3 abilities midgame to hit a triple kill, where as with jayce you need to do a lot of perfect qe's and make good decisions to engage in melee form at the right time or you will die, where veigar can go and just buy a 
Now lets talk about a matchup i REALLY REALLY hate to be a jayce up against
Who currently has a 2.5% winrate over jayce, the thing i really dislike about vsing a neeko is i can constantly poke her down with all my abilities and still not be able to kill her because her root, if she ever lands the root she could 1 shot me simply with that root and her other abilities keeping me in place doomed, left to die.
Another what used to be a good matchup for an example 
Jayce used to be my go to counterpick for vladimir with his early aggression and ability to poke down vladimir at the stage where he was weak, which is early game or was, now its jayce's weakness, together with midgame, and lets hope you dont have to make it to late game being the jayce, with that being said vladimir right now has a 5.74% winrate over jayce as he is able to outsustain jayce with ease, he is able to outpoke jayce as afther the q damage at level 1 got nerfed to be 55 and level 2 105 you as jayce simply do not have the damage to poke dorans shield vladimir down in health enough for you to be able to all in him and get a kill, even if the vladimir is a worst player or lower elo for that matter, you as jayce with thousands of hours in practice tool will get outpoked outsustained and when vladimir reaches level 6 he nukes a teamfight with his ultimate, where as jayce all you can do is poke with q e because if you melee jump in to a teamfight you are instantly going to die.
And now i get what ur saying, but jayce's q has gotten a 20% increase in 9.14 but, in 9.11 which you probably forgot to take a look at jayce's q damage got nerfed by that same 20% of his bonus ad ratio, where his q has also received base damage nerfs and to make it even worst, for people who dont actually want to spend the time looking at it or those who will and will agree with me here.
jayce's acceleration gate amplifies his q damage Meaning that the lower his q damage is, the less the damage gets amplified as the damage afther it gets amplified is based on jayce's total q damage from the ad ratio's added ad damage and the base damage combined together which is amplified. because it is amplified by 40%.
this means that if jayce q's base damage gets reduced from 115 to 105 jayce's q e also does less damage, a difference of 4 base damage on his q e so before this nerf it would be 161 base damage on his q e afther it is only 147 base damage but then they also gave him his normal ad scaling back, which you wont really notice untill you have finished a ghostblade or a second or third full item which you cant afford because you do less damage at level 4 where you have 2 points in q which is where it now is 105 base damage, or 147 damage for a perfect q e on to your enemy laner.
you got your full combo in with ignite, they dont die because you do not have the damage to kill them so this is a big problem because jayce has no late game scaling or to put it simply beyond terrible lategame scaling as he was designed to be an early - midgame champion where now arguably some of the worst early game champions such as cho gath and vladimir outdamage jayce and outsustain his damage with ease.
I have personally played a lot of jayce, and afther 9.6 skill matchups became losing matchups, so i started to only pick jayce in to jayce favored matchups which i considered to be
but both of these champions outdamage him in the early game, get a lead in the midgame and then have very strong skirmishing and teamfighting that
lacks the damage for.