The Storm Bull cultists are violent and dangerous, and a result are feared. But among the praxian nomads they are loved for their willingness to sacrifice themselves against Chaos regardless of the odds.
Among the civilized orlanthi the attitude towards Storm bull is more nuanced especially among the other Lightbringers beyond Orlanth (who has the closest ties to Storm Bull). Orlanth loves his brother but his companions are often more neutral.
What about in Lightbringers: Orlanth defeated Storm Bull soundly using only a lariat and a sharp stick? That’s certainly a story. But the cult behavior is more than any given story. Especially one likely not important in Prax (and first experienced by Gorangi Vak in the second age).
Are they like big scary biker gangs? The key difference is that unlike any 1% gang, the Storm Bull cult has an objectively really important social function – to sacrifice itself fighting Chaos. And in Prax (and even parts of Dragon Pass) Chaos, in the form of broos, ogres, scorpion men, and other monsters, are a real threat.