Slowing the ruck never became a tactic until quick play-the-balls became the end (rather than just the means) of most attacking play.
I remember an article from the mid 90s, where Craig Weston talked about how when he arrived at the Roosters he had the slowest play-the-ball in the team, but at the time of the article he had improved to have one of the quickest. Prior to joining the Roosters he had never even heard of the need to play the ball quickly.
So at that time there were obviously some clubs looking to create an advantage through quick play-the-balls, but there was also quite obviously many others who weren't. And now we have the situation where a team would rather concede a penalty than a quick play-the-ball.