Who benefits?
Interesting question as you say there is a right wing inclined free speech section who are very interested in culture wars.
Yet there is also a centerist liberal section focused on free speech and a section of old school leftists [people interested in material conditions over identity issues] who want free speech too. All of these people benefit.
Because what you are ignoring here is the internal war inside all the political parties. As you point out the new official Labour line is that women are adult females. In this they are aligning with the position of Labour Women's Declaration though not admitting that. The new position are also saying the TRA faction inside Labour ARE WRONG. So advantage LWD because in Starmer's Labour defying the party line is a risky prospect.
This is in fact a huge win for those fighting the internal war. Because once you admit women exist you are destroying Trans attempts to take Women's Officers positions in local CLPs a long term aim of theirs. Also crippling any attempt to get rid of the many gender crits in Labour. You also encourage gender fanatics to leave the party.
So getting every Labour candidate in the election to say women are women cripples TRA attempts to subverts Labour. In the inevitable parliamentary battles over women's rights to come it means that many Labour MPs will have been forced to say they think women exist. They can backtrack later, but it will on record. Because this is as much about the 2028/9 election as the one in 2024.
Likewise for those fighting in Liberals, Greens, SNP and the Tories. Because don't forget the TRA faction inside the Tories still exist and are sabotaging attempts to get biological sex recognised as much as possible.
It forces candidates to declare positions and this helps in the internal battles.
Obviously only a small number of people are going to change their vote over this so in that I agree it doesn't matter that much.
In the wider battle over gender though this is a massive thing though. Because it makes it clear there is a war between biological realists and gender idealists in Parliament, NHS, schools and everywhere else.
This isn't just daft women going wait a second people are saying I don't exist and that is important. Some of our MPs actually believe this. Some people think sex isn't real.
You can easily find out if individual MPs are institutional religious or not. This is just as important to know.