If, for example, Hiruzen used this. What then? Perhaps, and just a hypothetical here, it would be several normal sized fire-ball Jutsu cast in succession. Maybe they are heatseeking when cast like a higher rank Jutsu or with a higher proficiency. The one crime committed with this one was that it was never coupled with Amaterasu. That would have been terrifying, even more so than the Amaterasu Great Fireball.
