not sure you can build a rugby game around taking conversions!
It's pretty realistic - The modern game (well, for the last 20 years) is all about the boot (unless you're New Zealand). The running game is just to get you in range.

A good kicking system would be a good start: drop in an analogue-stick-only pass and move system and you're on the way. For me the most important thing for a rugby game is to control the direction of play rather than the players directly, if that makes sense: Madden worked this out years ago, making you feel skillful because you're directing play, rather than moving the player (which is kinda boring).