From Quendi...
I suppose such a study glosses over people like Isaac Newton...
No. A regular study takes a random sample from a population. If believers with the mental acumen of Newton or the others you listed were in the sample, they were included. If not, they weren't. No glossing over involved.
In any case, it's not very useful to list a whole bunch of clever belivers: there are a lot of clever non-believers who could be listed too.
I like to think that since I possess two college degrees (one in mathematics) and am involved in public education, I would be considered to have above average intelligence.
Neither has anything much to do with intelligence. Degrees are intellectual endurance tests, not intelligence tests (but few dullards achieve degrees in mathematics). Involvement in public education is meritorous, but again it is not a measure of intelligence.
By the way, you do not seem to be writing like someone with tertiary training in the mathematical sciences could be expected to on a statistical report: you wrote from emotion, not understanding.
If you want to believe that religious people are stupid, you can certainly find all kinds of data to support such a conclusion.
I'm not sure there is any reliable evidence for the proposition 'religious people are stupid' at all. But, in any case, no one has put that idea including the study's authors and those commenting on it. Only you did.
But I think it is equally important to point out that those of high intelligence have also committed atrocities against humanity. Their learning did not stop them from formulating weapons of mass destruction, drawing up plans for genocide, swindling governments, societies and individuals and other crimes.
Intelligence makes it easier to work out how to do things like split the atom, make a nerve toxin or get away with huge crimes. Intelligence is a different thing to good sense or morality. The observation is irrelevent.
This study reminds me of the old saying, “When you point a finger at somebody, it is good to remember you have three more pointing back at you.” Those eager to impugn believers would do well to remember this.
No one is impugning anyone, simply noting the relative level of measured intelligence between believers and non-believers. Folk wisdom has its places. Rebutting a properly conducted survey is not one of them.