@Invigorating being a jobber means being a character who's set up to win a fight but ultimately fail massively in order to show off how strong and cool the other characters are instead. think vegeta in dbz: he never wins fights, he just gets beat up so we can see how strong the villain is, and then goku can save the day.
as for disliking this part, i wouldn't say i "hate" it, just that i've been underwhelmed by everything after vitamin c. i never liked mamezuku much, and would've been more interested if araki had focused more on the characters he'd already set up rather than continuing to introduce more and more of them. it's got its moments and the art is great (if a bit busy and hard to tell what's going on sometimes) but overall the first half of jojolion was just better for my tastes.