'Second Wind' is a very badly designed rune -- Heals best when dead
There is no problem with the numbers, the numbers are perfectly fine each game. The problem is the 4% missing health healing.
Second Wind: After taking damage from an enemy champion heal for 4% of your missing health +6 over 10 seconds.
So If I'm missing 200 HP this rune heals me for 14 hp total in 10 seconds, which is a very long time... I can even not take this rune, replace it with 'Conditioning' and not notice any difference in regeneration. Because this rune heals on % HP you would think it would be useful late game but it does absolutely nothing, no impact simply because it heals based on missing health. Basically it heals best when I'm pretty much dead or have to return to base, what's the logic in that?
Why 4% missing health and not 2% of my max health for example?
Just like 'Font of life' heals allies for 1% of my MAX health, 'Second Wind' should do the same. If 'Font of life heals' for 1% max hp + 5, in 2 seconds. 'Second Wind' should heal me for 2% max hp +5, in 10 seconds.
Not only it does now what it's supposed to do, instead of healing me at full effect when I have to return to base, but also it's a useful rune late game which lets me regenerate poke damage.