I can accept that Sorcerer's believe all that crap about them having gone sane and are now free of their limiting human perspectives to see reality as it really is, but I think it's obvious that this is all a bunch of rot.
If it were the case that sorcerers had gone sane then societies with sorcerers would have out competed the ones that burned them alive and otherwise developed social safeguards against the use of magic. Were the sorcerers are free and sane as they imagine themselves, and were they simply clear eyed scientists that now saw reality for what it was and had therefore the levers to use to create new hitherto unimagined technology, then societies would have prospered from the presence of sorcerers as much as they prospered from the presence of any other rational science.
But the entire Cthulhu mythos is based on the opposite being true. The mythos universe is very like our own and knowledge of the mythos is confined to a few people on the very edges of society. The societies that endured, and built, and prospered are the ones that blinded themselves to magic while the ones with access to magic quickly extinguished themselves in cataclysms that all but erased them from existence - and the survivors appear intent on erasing even the last vestiges. Every complex human society from the Code of Hammarabi on has deliberately called down doom on the practice of sorcery and applied to it the death penalty, and the more they have avoided what we would deem 'superstition' the more they have prospered. Based on the external evidence, virtually every society and independent race, whether on this Earth or out in the unfathomable vastness of the stars is absolutely doomed by knowledge of much less contact with mythos beings. A great many races are on the Earth a refugees fleeing from the ruins of their own civilization which resulted from the outcome of their own sorcerous practices. I can't imagine that they are here entirely by accident. Earth is a refuge of blindness in the midst of the cosmic horror. A probably brief anomaly of life existing despite the cruelty of reality, and certainly not because of it.
In short, Nyarthalhotep and the Great Old Ones may encourage the belief that following down the paths of the knowledge they are promoting may lead to freedom and understanding and sanity, but all the external evidence points the opposite direction. Based on the external evidence, we have to conclude that the statement, "Then mankind would have become as the Great Old Ones; free and wild and beyond good and evil, with laws and morals thrown aside and all men shouting and killing and reveling in joy. [The] Old Ones would teach them new ways to shout and kill and revel and enjoy themselves, and all the earth would flame with a holocaust of ecstasy and freedom" is at best a half-truth, and most likely a sort of baited hook upon which to catch the species. This holocaust of ecstasy and freedom is foredoomed to last a very short time indeed, before the entire human race is extinguished. The Great Race of Yith has foreseen the doom and extinction of the species and its unsuitability as hosts, knowing that eventually the race will awaken or help to awaken or suffer to be awakened things best left undiscovered, and at that point it will all be over but the being eaten alive. No period of happy immorality, supernatural power, sanity, and freedom awaits.
The investigators on the other hand are the informal, unacknowledged defensive mechanism of the species. The part of the species that sacrifices itself by devouring the knowledge of the mythos and in the process destroying it and themselves. That is actually the only sane response, and the only hope that humanity will stay free.