Duel rankings are weird. You can crack the top 25 without beating anyone good, just offer ranked duels to peasants with 1500 score. You'll get 1-2 pts per win. Obviously you'll be severely punished if you lose any of those matches, so you need to stay away from people that can beat you by "getting lucky"; i.e. bar mace and other knockdown weapons.
For instance, there are many players ranked below me that are vastly better duelists (Mazrim, Tornkik, Eggo, KingChris, Tianyuan, Sauce, Jona, etc.) I'd give any of these guys even odds to beat anyone in the top 25, but they obviously don't take duel ranking seriously or they'd be ranked higher. If you are gunning for the top 25 and face one of these guys, you'll be faced with a situation where a win doesn't give you many points, but a loss would cause you to lose many points. But they are very difficult to beat, so the risk/reward proposition isn't there.
So in other words, if Top 25 duel ranking is your goal, it's more important that you duel the right people (scrubs you will beat 100% of the time, and the occasional top-25 player that you match up well against) than actually being a good duelist.