Actually, I think that post points out what the real problem is exactly: fans are fine with one-sided climactic battles, but only because when they happen, it's usually to set up an ongoing rivalry. The first fight gives us a taste of the enemy's power, showing us what the loser has to improve to match and driving them towards that improvement. In Baccano, the series is cut short at that point, so we miss the rivalry part and just get the first one-sided fight. As a result, it's rather disappointing.
Of course, all they really had to do to fix the issue was let Ladd land so much as ONE hit on Claire in the fight, since that would have been enough for Ladd to prove his point.