Completely stuck on a new mariadb-server initialization

Everything I can find suggests that host.frm should be created first-start in the datadir.

Whatever suggested that to you is flat out wrong. The system tables are created when you run mysql_install_db.

MariaDB official docs: Installing system tables (mysql_install_db).

In order for mysql_install_db to run for 5.5.38 on FreeBSD 10.0-RELEASE-p5 amd64 you have to supply: user, datadir and basedir. After mysql_install_db is finished, mysqld will find base and data directories without assistance. e.g.:

mysql_install_db  --user=mysql --basedir=/usr/local --datadir=/var/db/mysql

Please also note that the = chars for the parameters are required; but there is no error message if they are forgotten.