It almost seems like this Equality Act would (have) end(ed) up comparing an entry-level woman who's been on for a year to a man with 10 years on. While companies shouldn't promote a less-qualified candidate just because they're a man (or someone's nephew, etc.), that's not an issue of pay equality. (It's still an issue that should have legal repercussions, of course.)
You also can't necessarily say "because only 12% of the senior positions are female there's discrimination" - it's evidence that further investigation is warranted, but arbitrarily seeking something closer to an even split might just encourage companies to promote unqualified women. What's important is that a qualified woman is not impeded in her aspirations.
This strays a bit from the topic, but incorrectly implemented "equality" laws just end up insulting and even endangering women. My mom trained to pass using a man's standards for a very physically demanding job, and she can't stand when she has to work with some "dumb blonde" type (not necessarily blonde, just fitting the role) that can barely do the job. She says it's as bad as having to do the job alone.
Not to mention that poorly thought-out equality laws that to less women being preferred over men reinforce the social stigma surrounding women and the stereotypes that label them as needy princesses or as inferior to men. Pay isn't everything, and we need to be sure that the laws aren't just getting women more money at the expense of harming them in the eyes of their coworkers and society. If equality is going to work out for us, as a society, then we have to show those who aren't convinced that it's about equal skill = equal pay, not just equal pay. What's important is that employers make their choices as though they didn't know the employee's gender (except in those rare cases where gender is part of the job requirement, like acting), not as though they're trying to comply with gender equality laws just for the sake of the law.