I think it's that he can't deal with a partner on an equal basis.

If I understand your post, you tried applying solution oriented principles back then, and he didn't respond, he still fought against it. In fact, he stepped up his struggle with you and things got worse. Now, in this email, he expresses his wish that you change back to how you were back then, claiming that it seemingly offered hope.

Well, it did offer hope, but he decided not to pick up the ball and do something positive about his part in all this when the opportunity was there for the offering.

Now with your recent boundaries and keeping them (and I must say that I find myself agreeing with you regarding your take on most things), he's now realizing he liked it better when you were more willing to accommodate him, than now when you're asserting your equality. What his email suggests to me is that he still sees you as the one that needs to change and still doesn't see how it's really all about him having to make changes for this relationship to work.

He says how one big bad thing you do wipes out all the good little things, but he doesn't see how that applies to when he does his big bad things, like the mall abandonment incident.

He says he lives through your ups and downs, but doesn't see how you've had to endure his locking you in the laundry room, his kicking your head, his dragging you out of your bed, his putting his hands on you, his blaming you for everything he does, the list goes on.

I think your intent to ask for his participation to help repair is a way to go. Likely though, he'll argue and refute your reasons as to "all the above things that eroded my attitude and my conviction to fix things", since that's his pattern. And masked as a "sort of joke", he's already signaled to you that in your next fight with him, he's going to claim it's your fault things aren't working out; before the next argument has even begun we know how it will go.

Bottom line: he earnestly accepts going to a counselor, he earnestly works on his issues. Otherwise, he's just going to continue as is.