major problem with Sonos Arc Ultra - Sonos doesn't let switch to other speakers from TV menu

First of all thank you for providing another data point.  However, my reasoning is a bit different.

1. Even assuming they are not properly adhering to the spect, It would be not possible for large major TV manufacturers to cater to Sonos, since it might potentially break other products, based on the fact that users have been reporting problems with Sonos for years now
2. They have so many TV models they update every year it might  not be feasible to test and deploy it across such a large range
3. They will for sure NOT backport the fix for the older TVs
4. The potential fix might break all the other products that seem to do just fine 
5. Sonos has just a few products so it would be easier to test and deploy it
6. Based on your categorial statements, I presume you have a strong knowledge and familiarity with HDMI CEC protocol
7. “TV automatically defaults to the best sound” QED (The TV’s are  very smart now days and they know where the best sound is; even overriding user’s own choice in TV own menu to switch to say headphones or perhaps some bluetooth or phone; etc;.)
8. Back to reality: HDMI CEC is not just a TV feature per se. It is a protocol that has to be implemented and supported across all the participating devices on the HDMI bus where multiple device can negotiate and communicate with one another with numerous kind of commands and each device is of different and probably can assume multiple types (Playback, Recording, Audio, Tuner, TV)

I still do not see Sonos identifying this a a problem, especially since there is now a solution for headphone users; the Ace.

Especially for something which takes just a couple extra button presses to defeat.

CEC is a parallel buss that is shared by all HDMI connections in the system. It would be possible for a 3rd party (or DIY) device to monitor CEC traffic and issue commands to “amend” or “correct” behavior of seemingly rogue devices. However, this would not stop the rogue device(s) from then issuing their own amendments to counteract these corrections and the system could be trapped in a circular loop.

Another approach would be to insert a “CEC Manager”, similar to a CEC Blocker, into each HDMI connection that is able to manage the two-way CEC traffic for each device. Inappropriate commands could be blocked or replaced by appropriate commands. A major issue with this approach would be configuring and keeping this device up to date with respect to changes made by device manufacturers. The manager would need to be able to deal with past, present, and future devices, plus devices that are not running the latest firmware. Who would keep this device database up to date?

It’s not about the TV, it’s about being able to switch to Bluetooth headphones at nighttime when everyone’s sleeping. I shouldn’t need to buy Sonos headphones to use my Bluetooth headphones on my tv and be forced to unplug my Sonos beam 2 every single time wearing down the hdmi prongs and/or power supply internals. It’s ridiculous. 
 

it’s a simple fix, just let us POWER DOWN the soundbar via the app, so freakin simple.

So what’s the difference between using the app to power down the soundbar, and using a remote to turn off CEC on the TV?