How is it anymore “authoritarian” than starting in light mode by default lol?

It’s actually objectively the best option for the default, including over system default, for many reasons. It’s a better default than light mode because for dark mode users light mode can be immediately painfully bright, whereas even the most steadfast light mode user would take a few minutes at least to feel eye strain in dark mode, which is plenty of time to switch to light mode. It’s better than system default because often apps set to the system theme will flash light mode before loading the system option.