I don’t see anything wrong with that, and would argue that the current system is more fair overall than one without the gender distinction, because it’s more fair on average
What you should be comparing is the current system vs. the system without gender discrimination but with the addition of other factors which aren’t currently taken into account. You might be right in thinking it’ll be more unfair, OTOH insurers might be using it as an excuse to unfairly increase premiums for men, and that this will force them to reconsider how they assess risk.
You have to draw the line somewhere on what factors it’s acceptable to use. E.g. You can’t discriminate on the basis of race irrespective of whether there’s a correlation with higher/lower risk. Now that gender has come up there’s a big fuss about it because it involves change, but if in 10 years time someone were to suggest bringing back different premiums purely on the basis of gender I bet there’d be big opposition to it.