The wage gap is better phrased as ‘women, on average, do jobs that pay only 73% as much as men’. Which, in my opinion, is actually a far worse and harder to solve problem. Paying women the same as their male counterparts is easy. That’s why there isn’t really much of a gap in same profession comparisons. Getting women into more lucrative careers or getting Society to pay more for traditionally women dominated industries is much much harder.
To your question: The wage gap ‘myth’ is the misinterpretation of the statistic to say that women are paid much less for the same work.
The feminists argue by taking the average of all wages, and of course women produce less economic value overall when they're still the primary caregiver in most societies.