Welcome to the community. I am not running hero 6 yet but here is my take on this.
There is no “protection” for destroying or changing storage pools. WORM immutability is set at the shared folder level or in the case of hero 6 at the snapshot level as well. In a WORM setup, not every folder is set up to be immutable. You would not want it that way. You then could never delete or change anything on the NAS.
Additionally, immutability can be limited in time. So you can have a folder where files stay locked for say 5 days after they are written to. After that, the lock goes away. Other settings allow everything to stay locked permanently.
I don’t see that you would ever want immutability at the storage pool level. That would prevent you from being able to add space to the storage pool, etc.
WORM helps guard files against ransomware attacks. The files can’t be altered. Most of the time the bad guys who say get into your NAS want to infect your files so they can then extort you for money. They aren’t going to take the time to wipe your pools and destroy that. If they did, then they have wiped out all the files and they have nothing with which to hold you at ransom! So it’s counter to their mindset. Plus this stuff is desired to spread rapidly - get in to the system, spread your poison and get out. Pool wiping is going to take a lot more effort and work.
So this is my take on it and should not be construed as anything “official.”