I've been honestly thinking about that a lot in those days i passed without internet access.
Hayate is missed oportunity story wise. He "should" be stronger than he his.
The dude achieved black belt level of karate in a matter of days while amnesiac. (and don't come with this crap that ein is better, they're the same person, hayate didn't lose ein when he recovered his memories), he probably had the best mugen tenshin training his whole life, but he ends up being a jobber.
And then, truth hit me like an arrow. Hayate, besides the Raidou case (that was truly jobbing at its finest), is really unlucky, he seems to have all the skills, but he is the one getting caught in traps, and machinations, maybe his personality, anyways. The other thing, is that he is a plot device, he is the driving force of 3 characters, 2 of them being the main characters (Ayane, Kasumi and Hitomi), so, having him as the damsel in distress is often used to bring the importance of the main characters up, same way Jo Hayabusa ends up being a jobber in ninja gaiden.
If we go by feats, Hayate is a jobber, but from a potential, and skills standpoint, he should be higher.
Could he defeat Hayabusa? Nah, Ryu Hayabusa is like, meant to be the unbeatable force, he is leagues higher than anyone else, which shouldn't stop you from thinking that the other characters are powerful, i believe hayate is easily strong enough to kill a greater fiend on his own.