With 40.3% of my damage coming from Fireball and 7.8% of my damage coming from Pyroblast!, I got that with the 6% Fireball and 6% Pyroblast nerf I would have lost 5.9% of my total damage.
This number is subject to change, lowering the % overall nerf when movement is taken into account and you're forced to cast more scorches, effectively lowering the damage lost. But when considering Ignite DoT damage from Fireballs and Pyroblasts(!) as well as DoT damage lost from Combustions (especially with extra Combustions with T13 4 piece that I don't have) the overall % nerf increases. I also assume the Pyroblast nerf doesn't affect Pyroblast DoT.
However, as you mentioned the nerf isn't nearly enough to force us to switch to Arcane at all (except for the specific encounters some already switch for (Ultraxion possibly and Spine)),