Is there any fault in my saying that a comparative study between believers and atheists, which found atheists to be more intelligent, would yield different results if applied to Muslims, because other religions may be corrupt?

You must ascertain the study and the conditions of those on whom it was conducted, for the intelligence of minds is not the purity of souls, and not every intelligent person is pure, and this world is not the abode of recompense. This world is insignificant to Allah and is worth nothing. The Quran negates intellect from disbelievers because they do not benefit from it in the Hereafter, even if they achieved a high status in this world through it.