The reason why people think Brave is Yuusha, is due to the character of Yuu (勇) means brave. Agumon if I recall correctly also has relation to this with Yuuki (valor) which uses the same Kanji. If you use it to fit the character to Agumon, its silly to discard Erdrick on the same grounds.
I always see him as likely, but not confirmed. A lot of fanbases hype themselves up with little to no evidence and they end up fine, I can live without Erdrick being in after all I can expect Builders 2, DQXI S, Dragon Quest Monsters in the near future. In all honesty, DQ fans have it easier than other fanbases in this regard.