How important are Seers in reality? I've gotten in discussions where many people agree that Seers are pretty much useless and powerless

Rose Lalonde killed an ogre armed with nothing but a pair of ordinary knitting needles pretty much immediately after entering the game. Rose Lalonde found the secrets of the Green Sun and of the Scratch, forming the foundations for the kids’ entire plans in Act 5. Rose Lalonde found love on a battlefield and her hands have wielded both darkness and light and turned them into deadly weapons. Rose Lalonde, trapped with her friends in the middle of literal nowhere with a demon dog hot on their heels, nevertheless found a way to not only escape, but to journey to a new, wondrous land. Rose Lalonde knows more about the setting than maybe anyone else, and the tome of her collective knowledge inspired Calliope, arguably the most important character in Homestuck, to believe in the potential of reality.

Rose Lalonde is utterly fucking dwarfed by Terezi Pyrope, the girl who can sunder time by asking a question, who can know with absolute certainty the immediate outcome of a difficult decision. Terezi Pyrope, the girl so dangerous, Lord English sent his right hand Makara on making sure she was kept off balance through mind games and caliginy. Terezi Pyrope, who is so wise in the ways of the world that she can understand and manipulate people so well she’s repeatedly stated as the superior of Vriska, who is literally a telepath. Terezi Pyrope, who fights alongside gods and not only matches them in prowess but outclasses some of them (Dirk had some serious trouble in that fight). Terezi Pyrope, trapped and surrounded by dead friends in an offshoot reality in the middle of temporal nowhere, who found a way to turn game over into an easy victory by writing words on a scarf. Terezi Pyrope, who absorbed all the memories of Paradox Space and knew the world for what it truly was. Terezi Pyrope, the true protagonist of Homestuck.

And then there’s Kankri I guess? Yeah, he’s kinda useless, trapped in his own head and incapable of seeing and wielding his true potential. His alt-self led a revolution, which went surprisingly well up until it completely failed because the odds were stacked against him in a truly preposterous fashion. Not his fault really.