For fans of AOTC, there would be no Episode 2 w/o Jango, actually. The movie would stop right after opening crawl, because there wouldn't have been the subcontraction of Zam by Jango, no assassination attempt on Padme by Zam, who was subcontracted by Jango, no droid for Kenobi to follow to find Zam, no saber dart by which to discover where the clones are, yadda yadda yadda.
Had it not been Jango Fett, it would have been som other Mandalorian Warrior or Bounty Hunter, so why not make him both the clone template and Boba's father. That way you kill two birds with one stones, shed light on Boba's past, and acknowledge Boba's EU backstory that he came from a great line of Mandalorian Warriors.
I guess it's all am atter of opinion as to weither or not he was a fun character, however he was pivotal in the movie, as well as Episode 3.