if IQ is distributed on a bell curve, then you're mostly right, as most people aren't too different. almost 70% of people are in the middle range, i.e. between 85 and 115.
on the other hand, a difference of 85 and 115 might very well be what OP is talking about. i can't remember ever having a coworker who was so much more stupid than me that it would have been an issue, but i do know that i've had colleagues who were so much smarter than me that i suspect i might have been the stupid one in comparison - which would have been more noticable if our work had required higher intelligence (i only realized how much smarter he was than me when talking about private projects outside of work). so the difference in our mental capabilities wasn't necessarily a direct indicator of productivity and success with workloads where my lower capabilities were enough to get the job done, but that doesn't mean it wouldn't have been a stark contrast in a different setting.
i guess the people outside of the norm tend to specialize in work that either doesn't depend much on intelligence at all or selects for very high intelligence, so they're mostly among peers again.
on the other hand, a difference of 85 and 115 might very well be what OP is talking about. i can't remember ever having a coworker who was so much more stupid than me that it would have been an issue, but i do know that i've had colleagues who were so much smarter than me that i suspect i might have been the stupid one in comparison - which would have been more noticable if our work had required higher intelligence (i only realized how much smarter he was than me when talking about private projects outside of work). so the difference in our mental capabilities wasn't necessarily a direct indicator of productivity and success with workloads where my lower capabilities were enough to get the job done, but that doesn't mean it wouldn't have been a stark contrast in a different setting.
i guess the people outside of the norm tend to specialize in work that either doesn't depend much on intelligence at all or selects for very high intelligence, so they're mostly among peers again.