I need to clarify. Quite a lot of 'scientists' are terrible at putting the scientific method into practice. I try to exclude those people from the category whenever possible. I do acknowledge, though, that this will frequently lead to confusion.

A lower IQ of scientists overall would make progress slower, but generally wouldn't impede the self-correcting properties of the method.

The so-called scientists who don't or can't put the method into practice would have their ability to make clever but specious arguments impaired. Possibly the reduced nonsense-sensing of the scientists would still be more than enough to identify and exclude the reduced levels of nonsense.

With reduced IQ across scientists and 'scientists' both, it's entirely possible that there would be more scientific progress for the field as a whole. There are a number of necessary but not sufficient factors involved, and non-lethal but cumulatively-damaging factors as well. It's not obvious to me that the properties measured by IQ are equally distributed across the positive and negative factors; I suspect they lend themselves to the negative more than the positive.