I have to say I was initially very shocked to hear that you don't appear to have any control over the quantity of players who join the ruck, but it certainly does sound good being able to choose between pulling forwards, the nearest players or just leaving it balanced.
Totally understand and it may prove to be controversial with some. Ultimately though, if we want to preserve the ability to produce quick ball while giving an element of contest to the breakdown, this turned out to be the best approach.
As you know, in previous incarnations, your interaction at the breakdown was principally deciding how many players to add to the ruck. The system would then compare the relative stats of the players who had been added to determine the outcome. That's an over-simplification, but captures the heart of it. What we found was that users instinct was to repeatedly press x to add as many players to the ruck as soon as possible. Now there's slightly more thought and caution required when pressing x following the tackle.
We'd prototyped different players being added to the ruck, counter rucking, etc, but in the end this gave us the best balance of risk/reward and quick ball.
You will commit the same number of players on both sides of the contest. In that small window of interactivity following the tackle, there isn't enough time to select how many players you're going to commit and then to decide on the intensity with which you are going to contest the ruck. As soon as we bring both elements into play, we either slow down the production of ball to start the next phase of play, or we have to create controls of such complexity, that it all becomes inaccessible and stops being as fun.
The other thing that comes into play is that by forcing you to commit players to the breakdown on defense, you will have to work harder to stop line breaks, especially around the ruck. It's how we've chosen to balance the way the game plays.