There has still only been one official post made by someone who actually knows what's going on in the development department, and that post explicitly stated "Gladiator title". Notice that even if you refer to duelist/challenger/rival as glatiator titles the word "title" is still in singular.
We're pretty much left with
Option 1: the official blue post is correct and it's still possible to get challenger/rival/duelist from 2s.
Option 2: You can't get any titles from 2, which means GC is immensely bad at expressing himself and has the grammatical standards of a 6 year old. I don't point out grammatical errors unless they disrupt the meaning of the sentence, but seriously, learning the difference between plural and singular is probably one of the first things you learn in elementary school.
I'm leaning to the 2nd one myself, but there are so many contradicting messages flying around from more or less official sources that you can't possibly know.