Lucario's Dair beats out Marth's Up B. This is aided by the fact that Dair lasts a really long time. Marth also seems to ascend much faster than Sonic does.Except Marth has a pointy sword hitbox coming up, and Dolphin Slash rate of ascension is comparable to Sonic's up-b. There is a reason Marth has an advantage in this match-up (but not the only reason).
Bair also beats it out and lasts a long time, but is much riskier to land. However, it's usually a sure-stage-spike if it lands properly.
I won't even go into your idea that Lucario is at a disadvantage against Marth. I shall simply say that it is at most a neutral matchup. Only slightly in favor of Marth, at the most.