I was worried for a second that a tank jungler might actually be picked in competitive play. But I'm glad we're focusing on what really matters here -- keeping #LCSbigplays alive.
Please keep nerfing 
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is fine as always pls don't touch.
Sejuani is seeing more success than Lee Sin (hell, every other jungler in the game - including the 2 others you mentioned) across pretty much every elo in every single region. Her pickrate is fairly high as well, to the point where it's pretty close to Lee Sins pick rate.
Yeah, she needs some toning down. She was already strong and then was indirectly buffed through Cinderhulk (which pretty much every other tank jungler needed to be viable), so it makes much more sense to tone her down than to simply gut the rest of the tanks by nerfing Cinderhulk.
Hell, this change probably isn't even going to negatively impact Sejuani by much. The ult nerf only matters if you suck with her ult, and the W and E changes make her damage against squishies stay largely the same, but reduce her damage to tanks. Her early clears are also getting nerfed a bit. Yup, she's getting completely gutted, utter trash now GG Rito.
Stop exaggerating. Sejuani is stronger than Lee Sin right now.
Idk if it's just me, but even tho win rate is around 60% right now, she's one of the only one's(champs around 60% winrate before) that doesn't feel op in my opinion. I mean she does her job and is good at, does that make her op? not really. Some people champs can be good at their jobs(cough...cough) and be op.
Rek'sai is fine now after the couple patches of nerf she got. The Nidalee jungling nerf haven't hit live yet so we'll have to see about it. As far as the Sejuani nerfs go, they are pretty minor, meaning they are taking care to not overnerf her, so in this case, you are the one overreacting and not Riot.
LOL, how fucking high must you be to compare Rek'Sai to Lee Sin and Nidalee?
Nidalee literally just started to be in the jungle spotlight, Lee I understand, but yall can't get mad just because another champion does well in the jungle recently.
Winrate doesn't matter to the boards unless its Kassadin, Viegar, Elise, Azir, etc. Once a single champ is nerfed because of an extreme buff they got, the boards go up in flames and blame it on Lee Sin.
I mean I hate seeing lee sin as much as the next, but I will also say that he isn't as bad to deal with as I used to think. Maybe I'm just so used to facing him, but I find him easier to deal with than a lot of junglers. That said, I wouldn't mind him being nerfed out of existance as I hate that he is picked so much just so people can aspire to be insec. But still, he isn't really too op, just annoying to see all the time.
Amumu's win rate is starting to climb a little as well... better nerf him again just to be on the safe side.
got nerfed twice, and at the moment she is the one of the few champs that pays for her mobility (she is very squishy and is blind when burrowed, which she needs for her very slow dash).
She is still a good jungler, but she isn't strong enough to hang out with the likes of 
The only thing op about sej was that if you missed her ult, it still had an aoe slow.
It still does, but it's weaker. Basically this "nerf" just made her more difficult. But didn't lower her power by much at all if you're actually gud.
meanwhile zed...
She was already picked in competitive play. The complaints about sejuani's nerfs are really really silly.
