I think the high damage + potential ability is quite strong.
The concept is great tho.
Suggestions!
1. The bonus that farenheit gets for Fire Quanta is its ability, if you erase or swap that then it only does the base damage. Same as Hammer/Gavel when lobotomised. This means you can't have both the rune ability and the damage buff at the same time. Suggest ripping the damage buff altogether and just having it do 5 damage and the upped 7.
2. The Rune ability is useless if it can only be used once and is totally random. I suggest that the generate rune ability is based off of a target, or is randomly selected from elements you have quanta of. This way you have to setup what you want to use but it is more beneficial because of it.