I think this is it in a nutshell and it's not a concept that is new to any of us. Many women have expressed frustration at the "mental load"/"wife work" and here we have a man defining it from the other side as "free time".
He is currently suffering the loss of his "free time" as he is now having to deal with bills to pay, house to keep, admin to complete, kids to supervise, nurture and administrate. And it all takes time. He never had to do it before and more than that, it was invisible to him. He is very angry to discover that freedom comes with loss of free time.
On the other hand the OP is beginning to find herself with more "free time". It feels strange and alien right now but it will become more comfortable and normal. With her experience of keeping all the balls in the air, it will feel so much easier with less of them.
Ultimately the OP is enjoying finding some "free time" and the EXH is angry and the loss of his. This state of emotion will last some time I expect for both of them. He will, of course, blame OP because he can't possibly accept responsibility for his complete lack of understanding of his situation and the true cost of a relationship breakdown when children are involved. He didn't know when he was getting it so good. And, honestly? Hell mend him.