Why is there no simple DI / EI ?
That is an option but the OP intentionally wants to use an RTOS and the whole point of OS is to abstract away hardware, providing higher-level and consistent interfaces.
I personally think this line of thought is overrated because many of the "useful abstractions" are borrowed from non-RT OSes which again work against the long history and highly variable hardware of general purpose computing, where uniform standards are a necessity, and committees coming up with standards such as POSIX are the necessary evil. The end result is, code written for RTOS tends to take longer to write, is longer, adds overhead and prevents using of some features present in the microcontroller, and finally, doesn't necessarily offer the portability the designers wanted.
The proof is in the examples; the OP used the RTOS abstractions, but somehow come to the conclusion that adding a comment that describes what
actually happens on the low level, is necessary. I don't blame them.
As you say, on microcontrollers, atomic execution can be as simple as disabling and enabling interrupts. Parallelism is also, in most cases, extremely simple, to the point that constructing a typical "parallel" MCU application using interrupts comes easier than learning just the syntax to use things like pthreads, or any interface an RTOS provides. Of course, in some more complex cases, doing everything from scratch becomes more work, but MCU projects usually aren't that complex.
Personally, I'm not a big fan of abstracting away atomic accesses to "automate" the re-enabling of interrupts to the existing state; the motivation is such automation will allow nesting atomic operations, encouraging you to use such operations
anywhere because it's "easier" and "safer". No, atomic operations and disabling/enabling interrupts temporarily, in my mind, is a special operation which always happens with care and consideration, and is documented using comments. So then I just disable and re-enable the interrupts, and don't allow myself to create a complex condition where I don't know if the interrupts were already disabled and should not be re-enabled.
Low level programming on microcontrollers is a strength, not a hindrance, and I don't like abstracting it away. Desktop computing is different.