With engineers (in software and engineering) i found out that a lot of people are there just for the money. Those have no passion and will never be great regardless of the skill.

Then there are also different individual skills (like magnus carlsen is more skilled in chess than me) that are influcened by practice and talent.

Also for a lot of problems experience might be more helpful than intelligence so you dont need to be einstein to engineer a dishwasher (probably).