Hmmm, this sounds like a solution looking for a problem. More specifically, I think your solution is more complex than the problem you're solving. I too think that there needs to be some complexity added to the current system as is they want to really keep people interested. That being said, this solution sounds a little Rube Goldberg-esk to me.

Fundumentally, I think the problem stems from the reduction of effective roles. By restricting enhancement and enfeeblement to shadows of their former selves, they reduced the number of permutations you can use to affect the same amount of damage.

Global Cooldowns alone are not a problem, the problem is incentivising the use of all abilities. Your solution isn't really incentive, it's a slap on the wrist if you don't. Players respond better to the carrot than the stick - just look what happened when Blizzard rebranded rested EXP. I'm hoping that as new elements come to light, we will see more incentives to use various skills, such as cooperative damage bonuses in the form of Limit Breaks and more diverse effects from combos.