It's not just a measure for the state of sun in the sky, it's also a measure for the state of society on the ground. It's an arbitrary number in a sense, but it also strongly influences my schedule.
And yes, we could have all the schools and everything else open later in the winter than the rest of the year, but it turns out it's easier to change the clocks.
But the school schedule does already shift and it shifts later, so in the opposite direction. The policy trend is going in the opposite of what you want to achieve with year-long DST, you could instead vote for the status quo and have the same effect.