EDIT: for posterity - this is by design, when particular error is translated into OperationClientException, reason needs to be descriptive on its own merit.

Essentially when module does not have defined name attribute( or maybe even if it does not match directory?), upon creation of JDBC driver reason for this wont be shown:

14:09:08,620 ERROR [org.jboss.as.controller.management-operation] (ServerService Thread Pool – 43) WFLYCTL0013: Operation ("add") failed - address: ([
("subsystem" => "datasources"),
("jdbc-driver" => "com.mysql")
]) - Stage: (RUNTIME) - failure description: "WFLYJCA0041: Failed to load module for driver [com.mysql]"

Essentially just a failure because failure.