Tbh it still seems pretty useful as a vanguard for unknown dungeons, especially if it's just to take aggro
But yeah there's definitely a reason why there probably aren't many high-ranked ones. Still, there's no reason (so far) as to why it's considered so bad, though, since Rampart can clean up low level monsters and undead, which are requests that are nearly always in demand in these settings
Compared to Sword Saint? Sure, I'd get why people would be mad that he picked it over that, but as a general class, with randos shitting on him just because? Idk, it feels super forced to me