Do unused columns in MySQL/MariaDB notably affect performance?
Unused columns do carry a cost, but rarely one that most people will notice or care about in systems with well-written, targeted queries. If you are curious about testing performance and contributing in a meaningful way to the WordPress project, you might want to consider doing something like this:

Make a workable backup of your WordPress database. For example:
sudo mysqldump wordpress &gt; wordpress.sql

Note: This assumes you would create backups via a command-line. If you prefer GUIs, make a backup in your preferred way.

Drop the columns that you think you can live without:
ALTER TABLE wp_posts DROP COLUMN comment_status;
ALTER TABLE wp_posts DROP COLUMN ping_status;
ALTER TABLE wp_posts DROP COLUMN to_ping;
ALTER TABLE wp_posts DROP COLUMN pinged;
ALTER TABLE wp_posts DROP COLUMN comment_count;


See what breaks over the next few days. If WordPress is unhappy about something, it is not shy about telling the world that something is wrong.
Then, if nothing bad happens...

Begin modifying the WordPress API to handle those fields differently (if at all) and tweak the database to be more performant.


Working on a large project like WordPress can bring a great deal of satisfaction, particularly if any of your modifications are adopted by the core project.