depends on what you mean by significantly more difficult, if you are comparing it to stay at home mums then yes, ladies who are juggling career and home have it significantly tougher. But if you are saying that its significantly tougher for women than men, then I disagree, it completely depends on the couple. Obviously if someone is married to a king of the castle type guy then yes, but if it is a cooperative spouse than its a wash.
Additionally it is not always a matter of financial reasons to meet certain lifestyles, but of intellectual needs as well, Just because the option is available for the wife to stay at home does not mean she would want to take it, or that it makes sense. It varies by individual, their field etc.
The point is not what is right or what is wrong, as I said if someone wants to stay at home more power to them, but when such posts are made about all that stay at home ladies do, then well career ladies do that in addition to the careers. Only difference is when there are non school age kids involved where stay at home um is giving all that time to them rather than a nanny or day care. Although that time has to be quality as well which is not always the case.
as far as it not being sustainable, not quite sure about that. some ladies I know have run successful medical practices, research labs, and non for profits (real ones not mickey mouse types) for years while running a household. its challenging but not undoable, for some it would be for some it wont be.