User blog comment:SirAston/Thoughts and suggestions regarding Summoner Spells/@comment-5545048-20130808153408/@comment-5331854-20130808180046

The thing is, Barrier is selfish while Heal is for the whole team, so it makes sense for Barrier to grant more "health".

A possible solution for Heal could be this: It will heal a base value plus a bonus depending on missing health (somewhat between 0.3%-0.6% for 1% missing health, maybe?). Half of that heal will be granted instantly, the other half is over time.

This way, Heal becomes very viable in teamfights and a good spell for supports while also gaining a skillcap.