Restrict scourcebookssourcebooks
I cannot guarantee you that this will solve the problem 100%, but it seems likely that they are picking the combinations that lead to these numbers from a large number of sourcebooks, while the others do not care to or cannot find the similar build options.
If they always make the best character available, close in the boundaries of the game so that it ends up at least comparable to what the others are creating. I recommend a whitelist of books that players are allowed to use or a restriction on the number of books (like the PHB+1 rule in DnD5-AL) for character creation.
If they also understand that others do not have fun, this should not bother them. They are still allowed to look for optimized solutions/builds. If my gut feeling is right, their aim is not astronomical bonuses, but using the tools the game gives them the best they can.