Oh, you never disappoint! 
No formulae, but I can live with it, methinks.
What do you mean that she isn't a "high level orientated"? Do you mean that she isn't good in "high level" games (high skill levels?) or do you mean that she falters at high levels, compared to other Demigods?
The latter. High level in a pure RPG sense. Not high skill level, God forbid.
- Inner Grace is a newb trap. It does have its purposes for specific builds and matchups. But it's not that great overall, compared to her other skills.
- Healing Wind is basically the reason to play Sedna
Just my thoughts.
- Counter Healing ... varies drastically. It's essential in Sedna mirriors, but sometimes it's pretty much useless (with/against a Rook or when you have tons of AoE on your team burning the monks for you).
I usually find myself getting it at level 8. Intermediate skill opponents tend to rely way too much on monk healing, and they don't know Sedna, so it's basically a way to get a few freebie frags (tactically, that is; evidently, the strategical applications amount to much more than that). My approach is probably going to change the moment I 'go pro', though.
- Silence is probably one of the strongest Level 5 skills in the game. The first level is rather expensive, mana-wise, but each level after that adds a whole second for only 100 mana. It also stops sigils, shields, heals, teleports, and you can also use it as a ghetto shield III to secure locks or ports.
Just my thoughts. I get it at level 5, and from what I hear it's NOT going to change the moment I go pro 
- Magnificient Presence is underrated. It's certainly one of the very very few good level 5-10-15 passives in the game. It doesn't have quite as noticeable effect as, say, Healing Wind, either. However, it's really quite good for a variety of reasons.
Yes, I really like this one.
Additionally, a full MP+Silence Sedna with both Celerity flags + an Ice TB with Frost Nova III can completely 100% render opponent demigods from using skills.
For this reason, Sedna is actually not highly disadvantaged when games get to high levels.
By "this reason" you refer to all the advantages described, not to that hypothetical synergy with Ice TB and 2 Celerity flags, I trust?
- She is gold starved by her lack of AoE, and following a buddy around tends to limit her levels. So, she ends up having worse equipment and being at a lower level. Getting Nature's Reckoning in a 2v2 is a wise investment (in 2v2s, my first two items are Scailmail and Nature's Reckoning, then Scaled Helm and Unbreakables). 3v3, getting NR is a bit less important unless there is another Sedna or an Erebus is on the enemy's team. You can also invest in the 550 gold siege idols to help you farm. They do mark for gold, and they give you a little bit of damage too.
However, Sedna does a LOT of damage per hit, and has such naturally high regen that she can somewhat forgo pure late-game HP stacking. Eg, Askhandor + Narmoth's Ring on Sedna can be pretty powerful because it puts her regen through the roof, and she will crit for a LOT of damage. However, Girdle of the Giants is overall the best artifact for her (gives her attacks natural "splash" allowing her to actually fight people in a lane again).
This is extremely insightful and helpful. I've begun to think in this direction, but was a bit afraid of taking unnecessary risks (to hell with the rating, it just does not seem fair to experiment mid-game as far as my teammates are concerned). I'm actually going to fully rethink my trusty, but very standard and unimaginative item choices in this light. Thank you!
