Tbh I don’t think it’s a wild idea at all, I would say it feels more natural then not having all effects of lower level as well.
And your correct, it would take some work to make it balanced, but it would feel more natural to me and I would welcome the change personally.
Would also not mind more interaction between ranks in Finisher and damage from the Builder, giving someone a good reason to max a Finisher, maybe something like taking over the role of the synergy because otherwise Phoenix Strike being balanced around all effects at level 3 would almost demand maxing the elemental claws making the Phoenix build very skill point heavy.
So something like removing the synergies, but adding those effects to each Finisher (not as a synergy would be annoying if you need to max all Finisher to end up using just 1).
Simply something like each rank in Dragon Flight increases the damage of all charge skills triggered by it by X%, but ofcourse for each Finisher.
Or maybe other way around, Claws of Fire deals X% more damage based on the rank of the Finisher used.
Cobra Strike could then trigger increased life and mana regen for X second based on the Finisher rank, the increase based on the rank of the Finisher and the duration based on rank in Cobra Strike.
Just a thought, the intention is merely that maxing a finisher while doing elemental charge skills is more usefull.