In the name of Allah, the Beneficent, the Merciful.
I don't know if it's alright for us to judge the IQ of the beloved companions of the Prophet PBUH...
But I do believe, Islam is simplicity. And simple people understand it best. When Islam came to Makkah, the ones who questioned the religion and its authenticity were the ones who thought themselves wise. Wise enough to question the Prophet Muhammad SAW...
I once tried to comprehend the Hindus' view of death and afterlife...they have created such complicated fiction stories out of a simple concept that it'll leave the wisest people completely astonished, confused and baffled. Islam doesn't do that. It speaks to people clearly so that they comprehend the message. Some comprehend more than others, but nevertheless, they can comprehend.
Understanding and comprehension are things hard to understand themselves. You always think you understand something, but there are always days that come when you think, "Oh I understand it better Now!" To me, that's one of the mysteries of Quran. But like Allah says, out of the huge amount of knowledge, He's given mankind only little of it.
And it all makes sense, who knows if we'd ever be able to Understand everything He'd tell us. I for one to this day, imagine where Hell exactly is located. Sometimes it's few levels above the universe...sometimes...it's the blackhole...sometimes...I don't know. I'm sure even if I knew, I wouldn't understand...
No use of knowledge without understanding. All the scientists, the biologists, even little children know that, all the trees come out of more or less, the same thing, that is, Soil. And yet all the fruits taste different. How does that happen....Who makes it happen....
People of understanding know...and understand...