I'm not sure it's as unequal in general as you think it seems.
The majority of women probably don't have very long on enhanced maternity pay. For example, despite working for a good firm I only had 6 weeks at full pay and then dropped straight down to statutory pay for the next seven and a half months of paid maternity leave.
So there's a strong argument there that if most women are getting only the 6-8 weeks of enhanced/full pay, even with families who plan to split the leave then the woman is most likely to take those first 6-8 weeks off (few weeks before birth, physical recovery, establishing feeding etc).
So by the time the husband comes to take his time off, the vast majority of families would already be in a position where the wife would be on SMP anyway - ergo the husband should be on SMP too.
You also have to compare the different maternity packets of the two employers. The husband shouldn't get more money from his employer just because the wife would get more money from her employer, if that makes sense.
I'm not sure I quite agree that if, say, the woman was entitled to 2 months enhanced pay and then 7 months SMP, if her husband took over from her when the baby was 6 months old, he shouldn't then get his firm's 2 months enhanced pay as well. To me it's more that it should be viewed as a family unit: a few weeks/months at the beginning on enhanced pay, followed by a period on SMP, regardless of which parent is taking the time off.
So - If the mother's employer will offer enhanced maternity pay, but the father will be entitled to the statutory amount only, then it doesn't take a genius to realise that very many couples will be forced into a situation where the mother is the only one who can afford to take the time off. That's actually not got very much at all to do with women's employers v men's employers, that's just the different maternity policies of two different employers.
A parent of either sex should be entitled to the same maternity package. That's a good move forward. But it shouldn't create a position where a couple are able to essentially wangle more money because they take what is viewed as 2 separate periods of maternity leave, including 2 separate periods of enhanced pay, as this discriminates against people who aren't in a relationship.
I completely agree there is still an inequality there, particularly in terms of how many men's employers will view requests for extended paternity leave in terms of them as a good employer. But I think this is a good first step.