I will say that the mental load can be reduced or more fairly split if the other person is willing to step up. In our case, I still do the majority butI can cope becuase 1) DH has taken on at least some of it 2) he takes on a larger proportion of the doing and c) when he screws up he no longer attempts to make it my fault! This is a HUGE one and is something I see a lot. Men either blaming women because they were in the wrong place/missed something OR men throwing their hands up and going, "Oh, I can never get anythingright because she's so demanding" about stupid things like being expected to remember a dance class time, what's needed for the dance class, and how long it will take to get to the dance class!
Case in point to show how things have improved on this at our house. we (I) buy DCat's food in bulk. We have a container that is kept in the cupboard and we top up from the big bag into the more accessible container as needed. I did it shortly before we went on holiday and remember thinking, "next time I fill this I'll need to order more cat food after". So on Friday, when I went to find the cat food to refill, I was surprised to discover there was none.
It turned out the container had got lower at some point and DH had filled it up to use up the last of the big bag. great. But it did NOT occur to him to buy more cat food or even to mention it to me, as the person who usually buys the cat food. Not once. Not when he emptied the big bag. Not on any of the occassions he would have fed the cat and seen the container getting lower and lower. Nope. He just didn't think about it.
In the past, he would have been defensive etc. This time, he said sorry and then offered to make a big detour after work the following day to a shop that has a 50% chance of seeling what we need.