Hmm, a few interesting points. I don't believe that Firewave needs much of a buff tbh, it's really useful in team fights especially with the combo of Blaze. You also stated that it is not on the same level as other casters, but that is not true... Pyromancer has it's strengths, has some more armor and does some awesome fire damage... I guess to new players firing lightning bolts and forcing people to ride pigs is more appealing.
"I do not think there is anything wrong with a Pyromancer one-shotting someone with Firewave if he is directly on top of the player. If you play badly, you should be punished badly" - No skill should have the power to one shot another class, that is just wrong.
If you ask me, no it should NOT be reverted back to itself, from what I remember.. Last map during the 5th PvP tournament if you pay attention in this video you will see that 3 of SG's members have been 1 shot by Firewave. At the end of the fight and during the fight you will see that some people said that it was OP. (Haxnn was the Geomancer, sorry if I put you on the spot <3)
While I do like and enjoy how well thought out this thread is, I do not believe that it needs TOO much of a buff... I think that longer range or more fireballs would suffice.