I mostly agree with you. But I'm not sure that longer school days are the answer.
Ideally I'd like my kid to have school time similar to my working hours with before/after-school activities to fill time. Simply creating block time for students to work on homework/essays would likely improve education outcomes for many students.
But I'm thinking in terms of what children can take. I'm not sure a seven-year-old needs to work an eight-hour day. (I like the idea of leaving time for kids to do their "homework" while at school, though.)
If these "after schools" or "buxibans" (as I grew up around) became integrated into the school system itself that seems the most ideal. It would certainly kill off a secondary market of cram classes, for better or for worse.
Homework might not even be a thing at that point since they could just do it at school, as you mentioned.
Requiring employees to work longer hours is a bad look. The 40-hour-max work week was won with blood. (edit: by unions, funny enough).