I am more curious that OpenWrt doesn't set these (demux) settings. It feels a bit like looking for advice on ZFS tuning and finding out 10 years later that what you were told was completely wrong.

For what it's worth in your example there is a 10 year time span. What anyone was told 10 years ago about most things will have evolved with time, patches, major/minor code changes so if a configuration remains static for 10 years there will ultimately be room for some improvement just as the code itself and the hardware it is running on may have also changed.

Where this concept gets a little unnerving is the medical industry. Imagine if your doctor did not stay on top of the evolution on medicine and technology. They would confidently perform the same actions and prescriptions they did a decade ago even if it was now know that those things were not only wrong but also wildly dangerous and ineffective.

At least with routers and ZFS we are hopefully not using those to save lives and in the example in this thread it is just tiny change among hundreds of changes that have evolved with only marginal gains.