You don't get it because these rules are fucking complicated.
TA beat all 4 Elites, meaning he had to face Champ.
Hix wanted to quit because he was a moderator making TA, because there isn't any.
I don't know where in the rules does it say this, but Vitto says TA is now forth elite, but even though Hix can't quit during battle or this exact troll scenario happens (Even though ironically this time Hix didn't mean it).
You said how can the elite 4 have no champ. It happened before after the Nether Incident, just beating the 4th elite makes you champ. TA's scenario is different from the one i was stating earlier. Reason why I don't get Vitto's reason at the moment