Hence we keep these settings available. However, that doesn't mean we provide any support for whatever they do. We don't control Android to that extent.
Note: the "Extended power menu" option was added by us, and we placed it in Developer options because it's meant for power users who need easy access to TWRP or fastboot. Also not meant for casual users.
I don't know the ratio of rooted devices running your roms but all of them probably use TWRP to install a new rom.
And everybody can use it to make backups/restores because it's the more efficient and reliable way to do them.
I use it to backup my stuff at least once per week, and the ability to reboot directly in TWRP makes it less fastidious.
I believe that numerous enough of your users need an easy access to TWRP for the Extended Power Menu to be more accessible than in the Developper options.
I agree with you about Fastboot though but even if somebody that uses this feature to boot to fastboot by mistake should not cause any damage and quickly realize another reboot is required to get to the targeted place.