Thanks for the comments - we are thinking about this a lot.
The main issue is that we are trying to give advice that has taken us years of study to understand, and yet the software is in a state where some people feel like they are losing control (they don't understand it or it feels too inflexible), and that's no good.
We are treating f.lux as a promise to help most people sleep better, and we take this really seriously. I think there is another path where we just do "what looks better" and don't take the sleep science seriously, and then you'd be in control, but we might not be able to do as much good, and we couldn't make it better over time.
As @nothreek notes, we are not doing a good job for shift work yet, so often people on these schedules are more expert at their schedule than the software is today.
Regarding adopting "always-the-same clock time" schedules: people adjust to the seasons very differently based on their biology and location, and this is the number one reason we don't have a "clock time" setting for adjusting nighttime lighting. This has been a really contentious decision - but for most people, we think this number should change throughout the year and based on your location and travel.
If we made a really prominent setting (as some companies have) where you have to choose "change at this time", then we would have to respect that setting forever, even if we later realize it's doing a very bad job in the winter for some people, or for people at the edge of a timezone. And actually, we are about 99% sure this is true - lighting that doesn't adjust with the seasons is going to screw some people up. So when there are things missing, it's because it ties us into a solution we think would be wrong in the long term.
There are indeed people who actually do know better, and we should not prevent full customization for them, but the interface is making that difficult because 90% of people do not dig in like that (they use the defaults), and so we are avoiding settings that would prevent us from doing better in the future. But we should use the wisdom of people who are very aware of this to help solve the problem.
I am sorry we are slow to ship the newer flexible scheduling we are working on, but I hope we can solve many of these things soon.