Historically in Union you get very technique controlled micro skills.
It was the game where what kids were taught is what adults emulate in the pro game.
Bit like Basketball, you have proper ways to pass a ball, and then there are the innovations brought in by players.
Offloading in Union ala SBW who himself admits he copied Ali Lauitiiti was not seen till a league player went to their game.
In league the rule is anything that works is good.
I don't know where union is placed these days, haven't seen a game in an age so cant comment.
If you want to understand Katas problem get out in the backyard and throw some balls, you will see a marked difference in what side you prefer to throw, its not rocket surgery.