I don't see how this does not invalidate the original finding. The original was a statistical study based on an incorrect methodology which produced incorrect results and interpretation.

How can you claim the effect does exist if it has not been measured?

Indeed I do observe at times people who do not know much of a subject overestimate their abilities and sometimes I see people who are experts underestimating their abilities.

This does not however rule out that in many other occasions people who are inexperienced underestimate their abilities and people who are experts overestimate their abilities.