Hmm.
Can you run the mysqld command manually?
for me it looks like:
/usr/sbin/mysqld \\
--defaults-file=/home/kevin/.local/share/akonadi/mysql.conf \\
--datadir=/home/kevin/.local/share/akonadi/db_data/ \\
--socket=/home/kevin/.local/share/akonadi/socket-persephone/mysql.socket