That makes sitting all day unhealthy for me. And I know a lot of people who fidget like this! When I stand, I actually have to align my body correctly so that I can, you know, stand up. My core does work, my legs do work, I'm not standing on one foot or slouching because that's harder when you're standing.
I could learn to have perfect posture, but I'm 43, it's not cheap to teach an old dog new tricks. A standing desk is a great investment for me.
On the other hand, my co-worker both has perfect posture at their desk and also has bad knees. A standing desk would be more problematic for them. A quality, expensive chair (almost as expensive as my standing desk!) is a great investment there.
As you say, why are we always looking for the one way to do things? Even if things are factual, there's no reason that the same experience is factually best for all people. Factually, a standing desk is great for me. Factually, it's not great for my co-worker.
Also, maybe it's all in my head, I don't get that "afternoon drowsiness" at all since I started standing up after lunch instead of eating and then sitting in a comfy chair.
A friend who is a USMC veteran used to tell me that standard procedure in a briefing was: if you're tired, go stand up in the back. Super hard to fall asleep standing up. I bet there's a big chunk of that here.