Everything you're saying is fine and true; however, nothing you say actually justifies the 15kg FZR pentalty. (also, you refer to FXR when I believe you mean XRR).
Essentially, pre-patch the cars admittedly (by Scawen's own admission) were not balanced, and thus the several balancing changes were enacted to smooth the field.
With the added gearbox modeling, as well as tire changes, patch Y went about creating a level playing field, from the source. The XRR's fuel consumption, tire wear, and sequential gearbox are there to counter the FZR's 1-lap speed.
Exactly as unfounded as you claim this discussion is, We are saying the balance is wrong as-is.
As the ballast is not enough to majorly disrupt the racing, it will go unchanged, and it is an advantage the XRR will enjoy throughout the season.