^^ Jhin's kit revolves around his ult/passive,. His passive rewards him for crit, but the pen build is just so much better in almost any way and that's a problem.
And then he's gonna get nerfed for building lethality, so much, that crit build becomes too weak that he would ONLY build lethality and then lethality will be nerfed and he would be left in the gutter. Where have I heard this already? Oh wait, that's pretty common in Riot's balance decisions.
Jhin's automatic crit on his 4th shot is the problem. It makes his burst with armor pen extremely reliable; too reliable, in fact.
I mean the reason he's stronger with armor pen is the fact he has 3 strong AD scaling abilities and a % missing health physical damage execute. Q W and R all do great damage so hes basically played like an AD caster.
No, his passive rewards him for penetration.
His 4th shot deals % missing health damage. That is a huge additional base damage increase that does not scale with AD, AS, or crit. But it does do more damage if you ignore armor.
Situational builds.
When I fall behind in lane I have no choice but to go for the Lethality build because I won't do damage during the mid-game. However, if I am doing well, got a few kills, or had a safe laning phase I go into the Crit build because I can still do the same damage as Lethality.
The difference is when you are backing with 1.1k gold or 1.3k+ gold.
It is better to build the long swords for lethality than to wait for a BF sword because the pick-axe for I.E needs another 1.3k for BF or a useless cloak that is 800G for 10DMG(you can buy two long swords). That is wasted time and a lot of time farming instead of helping out in the mid push after you win your lane.
That is why you MUST win that mid-lane push after you take mid tower, or top tower. You can't just steal your mid or top lane's farm, that puts your mid or top behind and you are losing CS bot lane.
You aren't going to beat their mid-lane group with a cloak or a pick-axe, or just a BF sword. If you have a I.E when you rotate Mid, your ult will kill most targets.
The gold investment for a pick-axe and an cloak to complete the I.E or the items for the ER are not worth the time investment if your behind or not ahead.
So both builds are great but, depend on the game.
However if the game drags into late game, the Lethality build is garbage.
You don't have a rapid fire cannon, so your zoned very hard by tanks, and your ultimate does little damage to the front line and depends on the enemy team being awful. And even if you get a RFC, you do not have the Crit to fully use it, doing 200 damage to tanks per shot is awful when they have 2.5k-3k hp.
With a crit build, your Ultimate will burn the living hell of tanks, reducing their HP to 60% is important to start a fight.
Your forth shot is going to zone half the enemy team.
A Crit Build Jhin with 4 items will 1 shot any Squishy with a 1.4-1.6k brust + death fire touch.
That damage with a lethality build is only 820ish.
In the late game, killing targets quickly is more important than damage over time because in the current meta, many targets are mobile and escaping drags the game out too long.
The reason why pros use lethality is because the games end much quicker. They do not drag on for 30mins+, most end under 28mins.
But for the rest of us, games last in the 40min+ mark, so Crit builds tend to be more important.
Unless this is a flex ranked with friends, lethality will not help you if you had 2.5k and backed. You would have been better off buying that I.E.
I.E vs Ghostblade or EoN are night and day.
Try using training mode and test it yourself. Your ult with I.E will do 300-400 more damage than you would have dealt with lethality. (This is assuming you let the Death Fire Touch DoT do its work). And your forth shot will deal 50% more damage.
The same goes for MF, Black Cleaver + I.E is night and day compared to Black Cleaver + Lethality.
Jihn isnt meant to build crit though. He ALWAYS crits on the 4th auto, and the 4th ult shot, so things like
are really strong on him, but his skills all scale really well with AD, making lethality (armor pen) really strong on him too, since he can take out the squishies from a whole screen away.
If we saw someone like 
building lethality, then we would know that the stat and the items are over the edge. But as it is, the real reason that lethality seems like such a huge problem is that everyone in solo-queue plays champs who do not build armor, making it a damage v damage race in who can hit their buttons and skillshots first. And counterbuilding is gone from this game. Buying ONE 
makes all the lethality of a build worthless compared to a non-lethality build vs an opponent who didnt buy
His passive doesn't really reward him for building crit, it just makes it so building crit (aka the typical adc items) isn't completely worthless on him.
A large part of the issue is that lethality is vastly more cost efficient than crit.
I don't recall exactly but for the price of 
and
you can buy 
and a 
.
Meaning that by the time the critbuilds have barely completed their 2nd big item the lethality users are already building their 3rd.
And there is the fact that lethality items all have great stats. AD, lethality, movement speed and various passives. Those passive's increase the value of the items so much in a way that isn't reflected in the prices and the current state of the game is testament to this.
I think the meta for Jhin is actually: Ghostblade (which is generically good on every AD caster/assassin, and is getting nerfed), and then IE + Rapid Fire Cannon. There are much worse offenders of the all-Lethality builds imo; I'd target MF personally.
Doesn't matter what they do anymore to change armor pen. The game is such garbage compared to old seasons and they have way to huge of a pit to climb out of to be back to their glory days...I do admit the patches slowly make the game better but preseason completely destroyed league.
His passive also rewards him for raw ad, he isn't rewarded alot for AS which is a big part of the core crit items, he's nearly full physical damage, and his main contribution usually comes from W+Ult, which both scale of ad, cdr and pen. His laneing trades usually resolve around his forth shot, which crits without building crit, and his danceing granade which scales mostly of ad, cdr and pen. Jhin is an ad-caster, and his main power are the Ult, W and 4th shot, which all hardly profit from crit chance but hugely from lethality, cdr and ad. The only Crit item Jhin really synergieses well with is IE as the increased crit damage impacts the 4th shot for AAs and Ult, and Jhins usually get IE as 3ed item theese days. Why is it that hard to understand that lethality is ad-caster itemisation, and that some marksmen are ad-casters. If a champion like Jhin, graves or Lucian builts lethality, especially vs all the squishy comps running around(lethality is ment to work better vs squishys), there isnothing wrong with that.
If Jhin Is on his own dominant(which he was with ER+IE befor the Lethality buffs aswell), when that's an issue with Jhin. If Lethality overall looks to strong, then that's and issue with lethality. But the raw fact that ad-casters use ad-caster itemisation is not an issue. The fact that people opt for early powerspikes when the game is focused on early snowballing is hardly supprising, and the fact that people prefer builts that excell at takeing down squishys when most teamcomps either have only a single frontline and often enough non at all also is hardly supprising. People complain about item diversity, but once we finally have a viable alternative to Crit builts on adc, everbody looses their shits...
** Tl;DR** : There might be something wrong with Jhin him self, there might be ssomething wrong with lethality right now, however:
When the boards continue to refute that Riot knows this is happening and is backing down on damage creep in the next few coming patches. It's not like they haven't changed anything, but in fact they have. All the damage masteries are getting halved and people are still complaining about penetration. It's like they can't read the updates that are coming in the next few weeks.
Jihn always benefited from armor penetration. I learned this from playing Sion Support in Jihn botlanes.
When THIS happens.
And it's considered normal then I think there's a severe problem with itemization.
Dont let ranged champions benefit from lethality and problem solved. They can buy the variants of Last Whisper and thats it. Lethality items are supposed to be used by assassins not adcs. I hate the fact that adcs just ruin game balance by abusing everything. (Sterakk got nerfed, Armor Pen got nerfed becayse they abused it) Now they abuse Cleaver,Mallet,Maw,Lethality etc...
Simple solution: Make lethality melee only or makes it less effective for ranged
