Actually, that shouldn't be the case since 5.7: https://dev.mysql.com/doc/refman/5.7/en/server-system-variab... (and related: https://dev.mysql.com/doc/refman/5.7/en/server-system-variab...)

And on 8 MyISAM is mostly gone, not even the 'mysql' schema uses it.

Edit: Originally linked only to default_tmp_storage_engine).