The validate_parameters calls in message/externallib.php are mostly not doing anything at all.

validate_parameters returns the validated parameters with defaults applied. If you don't use the return from this function, you haven't done anything.

This is repeated through most of message/externallib.php.

example:

self::validate_parameters(self::data_for_messagearea_messages_parameters(), $params);

doesn't do anything at all.

should be:

$params = self::validate_parameters(self::data_for_messagearea_messages_parameters(), $params);

after which you have to use the returned $params['name'] - not the arguments to the function.