Dude, you're young and you're not fat. Add some of the conditioning drills in those articles a few days a week and you should be sorted out right-quick. This is no big deal at all, as long as you address it soon and correctly.
Kind-of-Side-Note: I'm not super-well-versed on rugby, but aren't you a bit on the small side? No offense intended, Rudy, but you might want to consider adding some dedicated muscle-building work once you hit the pre-season if possible. You might not be able to get taller, but you can always get wider. (I kid. Sort of.)
In those same months, how has your muscular bodyweight changed, and how has your performance on the field changed? (Those are rhetorical.)
You've always got to keep in mind... "what are my current goals?" When you're on the pitch, it doesn't matter that much if your power clean went from 215 to 225 last week instead of "just" being 205.
Like JFG said, you're not training to be a better powerlifter or Olympic lifter, so copying their style of training so closely isn't appropriate.
It's a little funny how silly you made yourself look with these statements.
John Broz is one of the most talked-about current Olympic weighlifting coaches in America.
He's not trying "to get better at jogging."
I do agree with this, to an extent.
If I were paid to train him for rugby, we wouldn't do both, because long distance/long duration jogging is a waste of time for most athletes; it trains energy systems that are unnecessary for the sport; and his issue isn't even a case of poor aerobic endurance, it's of poor general conditioning - and that can be addressed with much more sport-specific methods, as mentioned earlier.
For non-competitive weightlifters, power cleans aren't nearly as complicated as most people think. If someone can learn how to do a safe and effective squat, deadlift, and overhead press, they can learn how to clean.