Fortunately the community has addressed both these claims, although you need root to set it up (you can remove after).
An app on F-droid known as "Cryptfs Password" can change the encryption password separately from your screen unlock password. It also bypasses the 16 character limit, as the encryption key I used on my last phone was 27 characters. At the end of the day Android encryption runs using dm-crypt, so the same sort of rules apply. The 16 character limit is a UI limitation, and there's no technical reason for it.
* Note: I fully acknowledge that Google needs to do better here, as I would never assume a normal user could root + install Cryptfs password + unroot after, but at least for those of us who can, we can do something in the meantime.
An app on F-droid known as "Cryptfs Password" can change the encryption password separately from your screen unlock password. It also bypasses the 16 character limit, as the encryption key I used on my last phone was 27 characters. At the end of the day Android encryption runs using dm-crypt, so the same sort of rules apply. The 16 character limit is a UI limitation, and there's no technical reason for it.
* Note: I fully acknowledge that Google needs to do better here, as I would never assume a normal user could root + install Cryptfs password + unroot after, but at least for those of us who can, we can do something in the meantime.