Well the Star Wars media gives Jango that credit. Degree of power, especially in relation to other characters, is pretty vague/murky in Star Wars. However, if a character did something- well, they sorta did it.
So like Windu and Kenobi, for example, are shown many times to be incredibly powerful Jedi. One could say accurately, supernaturally so compared to most non-force users. If Jango survives a fight with opponents of that caliber he already is one the most exceptional individuals in the galaxy of Star Wars.
That is just the way Star Wars is written. Like that is what happened- Jango killed a lot of badass people, a really badass Jedi took him out with ease.