At the end of the day, Son's tackle resulted in a man getting a serious injury.
Yes, it seems the contact from Son did not cause the break; but had Son not made to foul; Gomez would be walking around today.
So, lets look a scenario where a ‘minor’ offence has different punishment depending on the outcome.
I’m in a pub. Somebody spills my drink so I push them.
- He stumbles and walks away. – No punishment.
- He stumbles, spills his own drink and slips on the floor – Pub will probably throw you out - Yellow card
- He stumbles, falls over and hits his head on the floor. He gets a concussion – Your getting arrested for ABH – RED CARD