Could not disagree more. It is all Xs and Os and clubs defend differently. Some hold their line and defend their inside shoulder. Some compress their line and challenge teams to go around them. Some just work with intense line speed and fill in the gaps. Some up and slide others shoot in and shut down.
Within the defensive line players have different roles e.g for middles set the line speed or be second/third in and wrestle. For backrowers some are organisers on the edge some are body guards for their half, some it is to harass the opposition half. You need to know your role and those around you. E.g. If you are a middle or half who knows the backrowers job is to harass the opposition half, you need to collapse behind him to protect the gap he creates by shooting out of the line.
Not only do you need to know what these roles are you need to know when to perform them.
Furthermore defensive game plans may be different within one team (typically for the backs) based on the skills of the players on each side and change based on the opposition they are playing.
If you are coaching get off your line and work hard for the bloke next to you, you are not coaching.