7zip silently leaves files unencrypted
Not only 7zip doesn't provide the same encryption features as p7zip, but it also silently ignores them.
If you install 7zip and ANY GUI compressor, like file-roller, then try to compress a file with password protection. The process will succeed.
But then if you open the archive, you won't be requested any password to open any of its files. Which means the user may be trying to password protect content that they won't notice they haven't been compressed.
Yet if you install p7zip-full-bin instead, this issue doesn't happen.
So probably it is better not to say that 7zip provides p7zip, and having p7zip-full packaged instead.