Yes, I too have been trying to work out where the Zephyr Project fits within this broader ARM embedded ecosystem development roadmap.
Nordic Semiconductor, for example, are now making a big push with their newer nRF Connect SDK, which is based on Zephyr OS and includes many new connectivity features like BLE Mesh and Matter. Only MbedOS TLS is included. So if you want to use these features you have to take the plunge. Having decided to do so I had to go through a whole install process (for VSC rather than SES IDE) and it was a rather convoluted process that lacks system maturity. Mbed Studio is now so much better.
So, in my opinion ZephyrOS is where MbedOS 2 was where everyone (as in vendors like Nordic Semiconductor) jumped on board as it’s new. This is a real pity as MbedOS 6.x is a more mature system and the documentation is now much better (although getting to code examples and libraries is still a pain point). So what is MbedOS doing on the connectivity front. What plans are there to include Zigbee, Matter, Thread etc. Are the hardware vendors giving MbedOS the cold shoulder or is it something else.
Is this related to some of the non core aspects, I wonder. For example, why only pyOCD as flasher/debugger with Mbed Studio. Is Segger J-Link excluded or is there some licensing issue or something else in the background the caused them not to facilitate and support J-Link being used. There was a comment in this forum post, but little has changed: Segger J-Link Support
So it’s all up in the air and the Mbed team need to do more to explain in their blog and promote MbedOS 6.x better.