I've actually owned Sej since she's first been released, she's just been so underwhelming that I neglected to play her until a few days ago. In my first 3 games as her, I played her in the jungle, as apparently thats the only way to play her. So I've come to the opinion that she's a mess. Her ult is fantastic, but that's about it. Her early clears leave much to be desired and even though she's in the "CC tank" category that Naut, Mumu, and Leona are in, she doesn't do it anywhere near ad well as either of them. I came up with what's (in my opinion) a modest fix to a majority of her problems

Frost: Sej's passive is only decent on it's own for chasing. to improve that, i recommend the slow increase at levels 6/11/16, capping at 25%. To improve Sej's pathetic jungle survivability, I also think that creeps and neutral monsters afflicted with frost should deal 20% less damage. Of course, to avoid being broken, Baron and Dragon would be immune to this

Arctic Assault: Sej's charge, while being a cool gap closer and escape ability, is pretty underwhelming when it comes down it. To repair this, I suggest, firstly, that the hitbox be widened to the width of Sej's boar. Second, the charge should apply in a small knock-back/up similar to Riven's Broken Wings AoE. Lastly, a shield should be applied on activation, Sejuani has no real sustainability, and this would fix this known problem. All of these proposed changes would give charging into a fight a much stronger purpose. These changes would also justify the skill having a ridiculously long cooldown

Northern Winds: The Aoe skill is used primarily for clearing jungle camps and it honestly doesn't do that very well. I suggest the base damage be improved by 10 at all ranks and the empowerment be improved to 75% over 50%. That would allow much faster jungle clears while not being considered overpowered.

Permafrost: One look at this skill, and you instantly know that it isn't actually used for the damage. This is supposed to give Sej's passive purpose, its a moderate slow that turns massive at later levels. while it does its job well, i feel that the range is incredibly lacking at a measly 350. Increasing this to 800 would allow Sej to secure kills for her team by catching fleeing enemy champions. *EDIT: It was pointed out to me that I misread the wiki, the range is actually 1000 on this skill already. Thanks to those who alerted me to this, you know who you are.*

Glacial Prison: I can say this is the one thing that needs absolutely no change at all, it does everything that Sej needs in a team fight. I love what it is right now.

As a person who was tricked into buying the double bundle...I hope Riot fixes her and makes her better than ever. Then again, this is Riot...and they don't care about half of the champions they make.

Although I never spend actual money on any content in LoL, I understand where you're coming from. I bought her on release day on my quest to own everything, and I've been thoroughly unimpressed ever since. She has the potential to be a CC machine, but she needs a bit of work, which is why I voiced my opinions on possible fixes for her. It's not necessarily about changing ratios or whatever, you just need to improve upon the skill itself to justify the damage and ratios given to it.

She has a great concept, just lacks damage, tankiness, has long cool downs and is just below par.

Looking at recent releases, we see Elise, Draven, Darius, Diana, Rengar, and Jayce (even after nerfs on most of them) all are in a completely different league than Sejuani. Sejuani feels like she's playing in the minors, has a great scheme, just can't pull it together. Yes she has games that she owns and just dominates, but I've played on teams with one afk and we win 4v5 with a huge lead. Having a few great games out of her in dozens means nothing.

Sejuani has a lot of problems holding her down.
The idea is finding the biggest problems she has and only fixing those.

I think the biggest one, related to her kit, is her difficulty to apply frost.
For example, if Her passive was changed to something like this
"Whenever sejuani takes damage, she applies frost, a 10% slow debuff on the source of that damage. Additionally, she can auto attack targets to put frost on them manually.

Doing this would significantly improve her jungle speed by allowing all minions in all camps to stay premanently frosted thus increasing her W AOE damage beyond the first target, making it possible to NOT take Q as early and instead level E, which would ALSO get a pretty significant viability boost.

It's just a suggestion though. (Frost would apply on ANY source of damage. Magic, over time, physical etc. This way she could block a skillshot and get an easier initiate on a now slowed target)

I really love the idea of this when combined with my initial suggestion to it, that would allow her to pass the debuff on to entire teams if she accurately plays her role. Doing this would allow her team to escape from fights as well as chase easier.

There are dozens of small changes that can be done, but something needs to be done, and hopefully it doesn't change her kit or what makes her unique.

Summon the reds!!!!!!!

I believe that the reds have effectively told us that there is nothing wrong with Sejuani, she can almost handle her own, she was never designed for the current Meta or any other Meta they will make. She was more of a concept champion for fun and not for competitive play.

She's so close to balanced that it hurts.
I'm scared if they buff her too much she'll become OP and nerfed to a worse state than she's at now. (Happened with malphite, god rest his rock soul)