Jhin hit a 47% winrate this patch. Alarms must have been going off at riot Headquarters, because he's now getting a neat buff in 7.12. But then we have Diana, who's been at the same winrate for almost 2 years now, and Riot haven't done anything.
I just wish riot would stop buffing based on the champion's playerbase size :/
Pandemic Punch4 votesDiana might need a small rework. She is always either over tuned or under tuned.
hater free zone3 votesDiana's biggest problem is her ult/escape potential fucking sucks. Every other assassin has methods of escaping after an all in. Diana just goes in and if she doesn't land her Q or get a kill, she's dead. Her ult is really just a crappier version of Akali's.
Magical Zoe2 votesBut Diana is a diver...and Diana suffers not just from having no escape, but there are far better picks than her in the midlane
she needs a rework.
hater free zone1 votesAll assassins are divers... that's what makes them assassins.
All those examples have ways of escape. Ahri's ult is 3 dashes and she gets a passive move speed, Akali gets stacks to use her ult more than once, and a giant AoE stealth/cc field. Ekko has a dash/port and rewind. Kat can shunpo to other targets or daggers. LeBlanc has her Deceive and Mimic. Talon has his parkour. Zed can shadow dance.
She needs a rework as far as how she expects to escape after a dive.
ProtestantCaesar1 votesNo, "assassin" and "diver" are two different things, and the main difference between them is that assassins are designed to be good at escaping, and divers aren't.
Diana was supposed to be a diver.
hater free zone1 votesI didn't know 'diver' was a distinguished class. I just figured diver champs were bruisers and I never viewed Diana to be anything like a diver or a bruiser. She always played like a shitty assassin to me.
Magical Zoe1 votesSo i guess
are assassins now? Since ya know...they are classified as divers.
hater free zone1 votesNo, I just didn't know there was a diver classification. I just thought she was a shitty assassin.
LunarStrike1 votesAll Assassins are divers not all divers are assassins.
the point is, those divers you listed are tanky and dont need an escape. However a squishy like diana needs an escape
chipndip12 votesDiana's issue is that, as a diver, her damage is front-loaded to the point where she bursts way too fast for any meaningful counter-play to exist when she's strong. Obviously they aren't going to buff her.
Jhin, however, has more counter-play, even when strong. It's easier for him to be buffed back to relevance.
FiddlesOnTheRoof1 votesHe's been in the dumpster for quite a while now. What is Diana's win rate?
LunarStrike2 votesJhin's never been a poor pick. Sure, he's had his ups and downs but all in all, he's maintained a pretty decent playrate. Diana bounces from 46% to 48% from patch to patch. Her play rate is around 1%. She's pretty much kicked out of the jungle too now
BALDG1VEN BOOMER1 votesJhin himself isn't a bad pick, it's his itemization that sucked ass.
Vapor Wave Vibes1 votesDiana can't be fixed with simple balance changes because of her kit. She's a fighter but can't do anything a darius, fiora, riven or any of the other fighters can making her the worse one and she's not an assassin do to low mobility. Really Diana just needs a rework while jhin can be fixed with just upping stats on his abilities.
Emerald Fang1 votesWell 
has a 54% winrate in all ELOs and Riot isn't alarm-bell nerfing that even though very few people play her.