Remove MySQL root after creating another user with all privileges

In this tutorial: link

After creating a new user with the privileges that I need, they recommend that I rename the root user to further ensure access, and a hacker, in addition to discovering the password, would have to find out the user.

Questions:

Since I created a new user and gave him all the privileges, do I still need root? Can not remove root and use only the new user I created?

If I remove the root user, do I need to remove the 3 that are registered in the User table (user table below)?

Why are 3 registered, not just 1?

+------------------+-----------+-------------------------------------------+
| user             | host      | password                                  |
+------------------+-----------+-------------------------------------------+
| root             | localhost | *DE06E242B88EFB1FE4B5083587C260BACB2A6158 |
| piucco           | localhost | *D8DECEC305209EEFEC43008E1D420E1AA06B19E0 |
| root             | 127.0.0.1 | *DE06E242B88EFB1FE4B5083587C260BACB2A6158 |
| root             | ::1       | *DE06E242B88EFB1FE4B5083587C260BACB2A6158 |
| debian-sys-maint | localhost | *ECE81E38F064E50419F3074004A8352B6A683390 |
+------------------+-----------+-------------------------------------------+

I recommend to replicate the users ( Host ) on all machines ( Users ), the default being:

CREATE USER 'usuario'@'%' IDENTIFIED BY 'mypass';
GRANT USAGE ON *.* TO 'usuario'@'%';
GRANT ALL PRIVILEGES ON *.* TO 'usuario'@'%';

CREATE USER 'usuario'@'localhost' IDENTIFIED BY 'mypass';
GRANT USAGE ON *.* TO 'usuario'@'localhost';
GRANT ALL PRIVILEGES ON *.* TO 'usuario'@'localhost';

CREATE USER 'usuario'@'127.0.0.1' IDENTIFIED BY 'mypass';
GRANT USAGE ON *.* TO 'usuario'@'%';
GRANT ALL PRIVILEGES ON *.* TO 'usuario'@'127.0.0.1';

CREATE USER 'usuario'@'::1' IDENTIFIED BY 'mypass';
GRANT USAGE ON *.* TO 'usuario'@'::1';
GRANT ALL PRIVILEGES ON *.* TO 'usuario'@'::1';

Check with your application if there is another type of mask for hosts .
If you really want to remove the root just run the script below, letting you know that the process can not be reverted via command, I recommend to back up the folder before executing the procedure.

DELETE FROM mysql.user WHERE  user = 'root';

If users are properly replicated with all privileges ( ALL PRIVILEGES ), the absence of the user named root does not affect anything at all, since it is the type of user that performs the action, not its name.