I love that earlier up in this same thread people are complaining about the magic \x sequences in postgres and this is how you do query edits in the mysql cli :)
I've got my biases, but whenever something like this comes up, I just make some popcorn and enjoy the show.
The complaint was that in psql the backslash sequences are a combination of client operations (\copy, \html) and database metadata operations (\d) [0], which while extremely rich, are a huge list and are not very intuitive to learn. Many differ on case (\df vs \dF). \des and \deu mention the mnemonics for why these are named that way. "External servers" listing "foreign servers" I can understand, but it seems that "external users" are not actually "external".
In MySQL the backslash sequences are commands to the mysql client for things that are implemented in the client and have to do solely with the command line client software. These things are not available using other clients. Vs things like listing columns and databases and functions have their own DDL language constructs entries and are queries in their own right that can be sent by any client software to the server and return iteratable results. MySQL is more like Oracle in this regard.
That distinction isn't obvious in psql and that contributes to a larger hurdle when using the command line client. This makes psql attractive to power users, as there are a lot of shortcuts for things that might require longer DDL statements to be typed or queries against information_schema.
It's not really possible to implement "edit the query I'm already partway through" with anything other than a magic sequence. Doesn't mean magic sequences are the right way to do everything.
https://dev.mysql.com/doc/refman/5.6/en/mysql-commands.html