I can't argue with much, or maybe any, of that. In fact here's a longer discussion on some of it:
https://budgetlightforum.com/t/-/41762?page=1
Nickelflipper had already had the same idea:
https://budgetlightforum.com/t/-/41762/38
And somewhere I mention I ultimately found an application manual indicating it as the expected use.
I gave some math on my low-ripple implementation here:
https://budgetlightforum.com/t/-/42480
But it seemed to not be a real common thing in BLF/modder flashlight stuff maybe. Then mountain drivers were using PWM output not PWM-filtered control, and it seemed that's actually what most LED applications needed. Both have their use. I think in the end we put both on the Texas buck. PWM-filtered control is far better for efficiency. In fact I don't see a ton of point in a buck without it unless you just need to get from 12V to 6V. There's a little point otherwise, but not a ton. However, especially for something like a Q8, PWM-output is still useful for moon modes, and that's why we discussed including both, and I think did.
It seems the LM3409 has been around lights longer than the Texas Buck thread too...
Although again, I didn't see it mentioned much before the Texas Buck, but I'm not sure. Richard at MTN recommended it though, so he was likely using it, and we did look at some other things, including synchronous drivers. In fact I now see we did design calculations for the texas buck for 1S:1S (Battery:LED), even at 4.2V, as well as every other possible combination. We just didn't advertise them all in the end, or I think we didn't, because, well 1S:1S for example seemed kind of pointless for that light. But we even had designs for a 4.2V powered board with an LDO just to control PWM filter.
I modelled performance in detail for different switching frequencies, voltages (battery state as well as batt/LED configuration), and power outputs, all with inputs for specs (Rds on, inductor resistance, etc etc) so we could compare efficiency and ripple for different parts. Multiple types of loss were calculated for every component. It was all in a configurable spreadsheet so I could try specs for different components and see performance instantly across a range of configurations. The images of the results of that are gone.
I don't recall the exact reasons we went with nonsynchronous. Simplicity, using a recommended part, not trying too much at all once, practical details of implementing various drivers that existed at the time, may all have been part but not all of it (there's probably some discussion there). As I recall specs for n vs p fets for different drivers were part of the discussion based on drivers at the time. But there can also be improvements at light loads/high duty cycles, and we certainly selected a good diode. Looking at my old spreadsheet it seems it did quite well on paper, and even not terrible in 1S to 1S but I'd have to review that and my old comments more carefully. The version I have in front of me says it could do 4.2V to 3.8V at 20 watts with 12% loss, 8% at low output. It's over twice better at 2S:2S though.
Anyway, 1S to 1S bucks are of course possible. I know Sofirn uses some small ones in some of their lights, two-board designs though as far as the ones I've seen, and they even sell their drivers, at least on aliexpress. I guess they aren't the only ones. One reason BLFers maybe haven't raced towards them for taht, and maybe manufacturers too, and it's true in those lights, is they don't do as well at reaching direct drive. So hitting those lumen records (and advertised lumens) isn't possible with them. I'm with rhd, for my uses, I prefer regulation. In 2S to 1S that's not an issue, and that, or 4S to 2S, were the main idea for the Texas Buck I think. There's also the fact that though really optimizing buck designs is a lot more work. There are a lot of types of losses to consider (even gate drive losses are quite significant, but are a tradeoff, like everything) and they change with operating mode and frequency choice, and in the end, 7135s are usually good enough to move on.
But some of the best drivers chips aren't so old, and maybe it's just waiting for someone like rhd to update us with one that keeps up the times.
Oh, and indeed the 1616DAC is a nice solution. 1616 was only barely coming into use in custom drivers then (2016) and it's quite possible that still just nobody has fully taken advantage of this avenue for reducing parts for a small hobbyist buck driver.