From what I've observed, there are two types of shit dad out there.
The ones who fundamentally care about their children and want them to have a happy life with all possible advantages but are happy to coast if someone else is around to offload the work onto. So they don't mind exploiting their partners but will reluctantly step up if they have to. Because they are committed to their kids having good parenting, even if ideally not by them.
Then there are the ones who start and end with "Me, myself and I". They don't care about their kids enough to put them first, or at least provide them with a decent standard of care and make them feel emotionally secure. If left to care for the kids, they just won't do it or will do such a shit job that the kids will suffer.
Yes, absolutely, if you are unlucky enough to co-parent with one of the first type of dad, walk out. Leave them to parent by themselves. Give them a taste of their own medicine and see how much work they can do while single-handedly looking after two disabled kids.
But unfortunately it sounds like the OP's H falls into the second category. Which means game over, really. You can't force someone not to be absolute scum, you can't educate them, all you can do is decide that you're no longer going to live with it and it can take itself out.