I'm a lawyer married to a lawyer. I will go through spells where I frequently have to work into the evenings (till 10-11 p.m. or into the small hours) and then spells where it's quieter. Weekends are usually fairly free. My husband's hours are shorter because of how he works. Neither of us are partners.
As to there being no work/life balance when you work in a successful law firm - it depends on the firm and the department and also the culture built by the partners in a given department, but your husband's hours do sound extreme even from a US law firm standard. As you say, he's a workaholic and he is choosing to work this hard because of the power and status that come with it and because of his long-term plan to retire early 50s. Of course, if he continues to work this hard, he may not make it to his early 50s (or at least not in a state that allows him to enjoy his retirement), a point you have doubtless made to him. But it sounds like he's in a particularly strongly 'macho bullshit' environment where the partners have created a culture in which everyone has to act like they're made of steel and have no needs outside delivering work for their clients. There are firms like that around and some people thrive there. Their families generally don't - or at least the families thrive without them. Also, frankly, working extremely long hours for clients is still easier than trying to entertain and keep up with 3 young kids so I am absolutely certain that part of it is that he just wants to avoid the effort which comes with looking after his DC.
You have to decide whether or not you can live with this situation but there's no point making baseless threats to leave since he's learned that you won't follow through. Of course, you want to avoid leaving but it does sound as if he currently sees no real reason to stop working the way he's working because he's not feeling the consequences of the choices which he's making for the entire family. It's hard to see what else (apart from a serious personal health crisis) is going to cause him to modify his working patterns.
You presumably have no income because you have become a SAHM because your DH is never at home. You are performing an incredibly important job but it is unsalaried. Since you're married, I think you would be entitled to maintenance from him to pay for the children and support yourself. I don't know the details but someone else will be able to point you in the right direction. So you wouldn't be without an income. But if not having an income troubles you, could you consider going back to work part-time once the lockdown is over? Perhaps you could put your DCs in nursery or some other form of childcare for some of the week. Or even all of it, depending on what you wish to do. Your H should share the cost of that. You should regard the childcare costs as an investment in your and your children's future (that's how I saw them).
Because in the end, I think having your own income will give you an independence which you currently feel you are missing and may help you create a family situation which is more acceptable to you.
(I hasten to add that I may have read it entirely wrong - and being an SAHM is an incredible thing to do and it's great if you're happy being an SAHM. But being without your own income does make it harder to get away if you are unhappy in your marriage).