I like this, kind of?
You've written a really good article and I enjoyed reading it. I suppose I just disagree with the philosophical point that Dr. Brown made. Not completely, but... well... hm. Maybe it's just better if I explain.
There are a couple ways to define what "50/50" in a relationship means. Dr. Brown took one of them (a definition where both people try to keep things equal all the time) and showed how that interpretation was damaging. And then she offered a better way of thinking about it.
But that's not the only interpretation of the 50/50 rule. A lot of people in the comments here have pointed out a better interpretation; it's one where, on average, both partners shoulder about half the responsibility in a relationship. You can fluctuate back and forth, talk when there are problems, have bad days and good days, etc... -- but in the end, both of you are invested, and you meet in the middle.
A lot of people don't have relationships like that.
For them (and I'm pretty sure their interpretation was around long before the one Dr. Brown used), I think the real idea behind "50/50" is that it was meant to be a safeguard against abuse. It was a language created by people who felt they were shouldering all the responsibility for a parasitic spouse, and they were trying really hard to explain what was wrong because their spouse wasn't shouting at them or abusing them -- they were just abdicating all of their responsibility for making the relationship work.
So, on the one hand, it's great that Dr. Brown has a more nuanced way to discuss giving and taking in a relationship. But on the other hand, it's a bit rude to act as if that's the only way to interpret the 50/50 rule -- it overlooks the struggle of a lot of people who used the language of equal responsibility to help articulate what was wrong with a bad relationship, and to develop the self-respect to demand more -- or leave to find something more equitable.