You are clearly questioning the need to go straight to a ruck, which is great, however the reality of this situation is dependant on how you are coached. In my opinion going straight to the ruck option leaves out the following elements of play:
- Pass to someone in a better position to take the ball forward
- Change pace and direction to run around and avoid the defender
- Hit the defender in a strong position, drive low to high, put them on their butt and keep going
- Hit the defender hard and pop the ball to a support player coming in close
- Hit the defender hard, go down to ground and pop the ball up to a support player coming in
- Hit the defender hard, go down to ground and place the ball (long arm) on the ground for a support player coming in to "pick and go"
As you can see, there are 6 things that can be done before even considering taking the ruck option, so having a game plan that merely reads, "get close to a defender then go down and ruck over" is severely reducing the attacking options and takes away any decison making requirements from the defence. If you always go to ruck, that's easy to defend - if you "mix it up" as shown above, they have to work much harder.
The six items above should form a "check list" in the head of the ball carrier; can I pass (no), can I run around (no) can I put this guy on his butt (yes) Ok here I go, etc, etc. Players need to go through this mental check list in seconds which is not always easy which is why we need to practice it and coaches need to allow time for this in their sessions.