1. My point was that standard linux should have those things too if it wants to be considered "secure". Default Linux isn't secure out of the box without a lot of work. It is more private than proprietary OSes but not more secure, therefore compromising your ability to safeguard privacy as a result. Linux is also a great target for threat actors because the majority of servers run Linux, meaning security researchers and cyber criminals alike are looking for weaknesses. I'd recommend looking into Android's Security model because it is interesting and gives insight on designing a secure mobile device. Stock Android suffers from OEMs not providing consistent long-term updates for devices, which 3rd party security hardened ROMs like DivestOS and GrapheneOS help to address.

Extra reading: see Whonix comparison table to see what they look for when choosing a base OS that can be later hardened for security. Note that some things in the table are not security specific but important for anonymity (which Whonix modifies to Kicksecure to better protect). Whonix is a security focused operating. Here is a comparison of different memory allocators showing their features for preventing different types of exploitation. Memory based attacks consistently are reported to be one of the most common types of attacks.

2. Here is a link to the Wikipedia page on Linux-libre Kernel. I'm not suggesting this should be the default, was just making a point that binary blobs may be needed in a kernel for compatiblity or security (eg updating firmware that is vulnerable when that happens).