So what? Jango Fett was a known Jedi killer, which was the reason why he was cloned, so the clones would be effective in killing Jedi in Order 66. He killed half a dozen Jedi whilst he was Mandalore. And he killed that rogue Jedi, Komari Vosa. Even so, he was a better than fully honed Mandalorian.
You do have a point though.
I'm speaking strictly from the movies, that was his only kill. Ya...you mean that absurd comic where he took on those Jedi bare handed? The ones who seemed to forget that they could use The Force, or the fact that their training seemed to have went completely out the window? Really think on that for a minute Beni....that comic was full of CIS/PIS...I am actually surprised its even canon with the way it was written.
He didn't really kill Vosa, Dooku did though yes Jango did fight her and beat her though he was outmatched by her Force skills and the like(though should note that Vosa was really just a padawan gone darkside). His only saving grace was his jetpack and weapons(moreso the former) though....infact he should have died before then and was actually saved by Zam.