BTW, if one is an apikorus for not believing that a certain perush was written bRuach Hakodesh, it would certainly help to have a definition of Ruach Hakodesh.
But I will give you some proofs that even the Avos did not have knowledge of everything, only what the RBSH wanted them to know.
1) By the Akeidah, if Avraham knew the outcome that he would not have to sacrifice his son, then what was the nisayon?
2) The pasuk says vYaakov lo yada ki Rochel genavasam. Yaakov who cursed the one who stole Lavan’s terafim, did not know it was Rachel, and that she would die young as a result.
Furthermore, the Rambam writes certain scientific facts that we now know are not correct, such as the existence of hard spheres in which the planets are embedded, the sizes of the Sun and Moon, etc. Does this lessen the Rambam in my eyes? Not at all, because he would be the first to say go with the science of your times, not of mine. (Remember that he writes in Kiddush Hachodesh 17:24 that any scientific or mathematical fact which has been proven even by a non-Jew, carries the status of Divrei Neviim.) The intellectual honesty of the Rambam is overwhelming.
So please define exactly what you mean by Ruach Hakodesh.
One further thing, if you mean to equate Ruach Hakodesh to Nevuah, then we are allowed to test a Navi by making him predict the future multiple times. (This is a halacha in the Rambam). Do you know of any gedolim today who would want to undergo such a test?