After playing this game for a few more days, I've come to the conclusion that you're all fucking wrong.
Since I hit level 31, I've been pitted against lvl 40-50 players who are equipped with all Super-Premium items and have stats like "Attack : 1300, Magic Attack : 1500, Defense : 1200, Magic Defense : 1100" ...players I'm hopeless against, since my highest atk/def stats are in the 600 range.
Maybe I'm the one who's fucking wrong; maybe these people having been playing since October and have found all these Super-Premium items randomly or through the monthly treasure maps and challenges. Either way-- if you didn't get into this game early, then once you hit lvl 31 you're fucked, because you'll be playing against all the veterans.