> people frequently argue that it is impossible to build a gender-equal team.

No one argues that. What is true is that it's impossible for everyone to have a 50/50 teams (because most fields don't attract precisely 50/50 men/women), and it also makes recruiting substantially more expensive if you hope to maintain a high and equal standard for both men and women. This is a consequence of the fact that, assuming skill distributions are roughly the same across genders, there are simply much fewer (in absolute terms) women of a given skill level than men of a given skill level in CS or engineering.