There are definitely measurable population-level effects, like increased traffic accidents [1] and heart attacks [2]. And given that its purported benefits are completely unsubstantiated, it's amazing that DST still exists.
That's just not how it works. it's much easier to have one entity say this is the time. having every business open up an hour earlier without some decree is not tenable because of tradition and change inertia.
the noon argument is not very compelling to me.
I go even further with this and say the whole world should be on the same clock. Who cares if it says 03:00 when you eat dinner or 17:00 when you eat breakfast - and think how much easier it will be to plan anything that spans timezones!
If you say you were up at 3 am, I know that was very late, no matter where on the Earth you are referring to. I don't need to adjust my sense of time whenever I change timezones. 12 is always roughly the middle of the day no matter where you are.
I don't want to like DST because it seems so inelegant. But it does give people an extra hour of sunlight. And I think that is a very desirable thing. There are a lot of mental health benefits associated with outdoor activities and exposure to sunlight. I have personally noticed my mood is very affected by the weather and whether I'm in sunlight.
Unless you expect all the Auzzies to move to the night shift, it just becomes more of a pain in the ass. You still have to line the phase of the day and timezones help simplify that by doing the work upfront.
You could switch to only using UTC outright for all your planning today. But even if you do, you'll find there is still a translation step of figuring out that business hours at location X are Y-Z UTC. Timezones make juggling the offsets easier, and also give you a stronger ability to roughly predict someone's schedule (like what time the business day starts, or not planning something during their lunch) just based on geography.
I'd also much rather work 7-3 than 9-5.
EDIT: I should clarify that this is nearly always the argument brought up against year round DST, so that children during winter go to school with sunlight in the morning.