This is awesome because I like reasonable solutions that let me be lazy.

I'm sure there are designers that love dealing with two themes, and will do beautiful work within each theme.

But I'm really fine with letting the computer figure it out. CRM, back office tools, admin dashboards... many clients are approving one design and dark mode is an afterthought. Why can't the computer just... do it for me, and do a better than passable job at that.