dune - Was Frank Herbert's use of Bene Gesserit in his plot ironic?

In Frank Herbert's Dune series what was the point of the Bene Gesserit in light of their motivations for existence and how their ultimate plans played out in the books? Does Herbert use their goals to ultimately make a point that they were fundamentally misguided, driven as they were by prescience? Or maybe does it go even further to the point that the Bene Gesserit should never have existed to begin with?

Take for example the Kwisatz Haderach. It seems that even the Kwisatz Haderach was never the ultimate goal of the sisterhood but was (for them) a necessary goal to reach some unspecified (does Herbert say?) further goal (perhaps an intractable quest for more knowledge might be one suggestion). But rather than propel them the creation of a KH rather turned back upon them, into an attack on prescience. It seems then that the Bene Gesserit were ironically mistaken in their quest for prescience, because the very point emerging from the God-Emperor of Dune appears to be the need to escape prescience, and thus Leto II intentionally marginalized the BG as part of his quest to save humanity which indicates that theirs was a foolhardy quest.

Had the sisterhood known in advance somehow that the whole goal of seeking a Kwisatz Haderach was going to end up only teaching them a lesson that a Kwisatz Haderach should not exist at all (nor any Reverend Mother, BG, or any other prescient individual - as I understand it) then it would have negated their reason for existence. Of course where the mind-bender comes in is that unless they had had a KH they may have never have come to that realization - thus hindsight is 20/20 (resulting in irony).

Further, beyond being just misguided, if in the outcome of the Butlerain Jihad the Bene Gesserit had never come into being how would the situation of humanity be much different than how it turns out in the Dune series? Does Herbert say anywhere clearly what the ultimate purpose of the Bene Gesserit was and whether it was attainable? It seems that only an escape from prescience was necessary in Herbert's novels to avert the threat to humanity, not the pursuit of it. Thus could Herbert be suggesting that the Bene Gesserit were not even necessary at all? If that humanity would have survived just fine without the Bene Gesserit is one of the implications of Herbert's novels then there is major irony here, since the outcome of the whole BG project seem to lead to an indication that the prescience underlying the BG order must cease.

So is Herbert's lesson concerning the Bene Gesserit an ironic device?