he was sexist by 70s standards too, he got called out for it in the 70s
Sure, but he wasn't nearly as sexist as many, many others. Countless are the tales of bosses demanding sexual favors to get/keep jobs, grabbing rears, fondling women, leering, harassing women verbally in the workplace, and more. Gary's comments, even the one doubling down against women's lib, don't rise anywhere close to those commonplace occurrences in 1970s workplaces.
From what was said in the quotes by the woman(can't remember her name) that worked for TSR, TSR wasn't like that. She found it fun to watch for the women in bikinis and call out when one walked by. At least until her three favorite coworkers left. She says that right after she was hired D&D exploded and Gary couldn't find the time to mentor her, not that she was hired to be a secretary and/or eye candy. If TSR(Gary) had been as bad as a whole lot of other businesses, she would be telling a very different tale.
Treating him like he was somehow among the worst of the worst of the 70s sexists doesn't accomplish justice. Without the understanding that comes with seeing the environment he came from and lived in, and understanding his human side, you can't really temper your judgement of his sexist behavior to the appropriate level.
If all you want to see is the sexist side of things, you are going to overreact and get pushback from the people who are looking at everything. Refusing to look at the human side or environment that Gygax came from is also going to pull the pendulum too far towards your side of things, and when it swings back, and it will swing back, it will swing back too far away from where it should be(and what you want), because that's how pendulums work. The farther towards the extreme end you pull it, the farther towards the other extreme it goes when it swings back.
Moderation, and that doesn't mean ignoring the sexism, but rather understanding everything and giving the appropriate response, keeps the pendulum closer to the middle so it doesn't swing as far or possibly at all.