To be honest, even convection has its issues, but for a level 1 talent if its completed it does a decent enough job for its existance.
That Fel Infusion needs a boost, i do agree with, but it should remain a rather simple one. And the idea for a quest is a decent one aswel. It however should not rely on globes since there is already a level 1 quest on this. It shouldnt even rely on Q alone either. I think a more themed quest towards the talent task would do better:
Passive: Kaelthas gains 0.5% maxHP regen per second while verdant spheres is active.
Repeatable Quest: Hit players with boosted attacks from verdant spheres (for W, the explosion does not trigger stacks).
Reward: For each player hit, increase the spellpower on boosted attacks by 0.2% (maybe it should cap at 25%. But consider that it takes a very long time to even collect this value → 125 hits), and still only affects the boosted attack (pyroblast is not boosted!)
For the passive it still applies healing (and actualy even less than what it used to be, but now can heal more over time. It might be insignificant during fights, but especialy when retreating it can add up to a decent HP value (1 minute out of a fight is 30% of the max hp). It makes it a more reliable talent in QM environments, but barely maters in draft.
The quest is also to give it a late game feature that at that point is welcome. 10% spell power on boosted attacks however is still low enough that its not going to become a major damage effect.