Metro_Knight
Smash Rookie
Falco also goes even with many mid tiers as well...marth will not be top 3 imo. He goes even with too many mid tiers to warrant being third
The difference is that Falco has medium-hard matchups with ICs/Pikachu. Marth is in the disadvantage against Diddy yes, but it could hardly be considered a hard counter. He also has a noticeable advantage vs. Wario. In my opinion, Marth at least has potential to pass Falco with MK out of the picture.
But, besides the Diddy/Wario thing and the IC/Pika for Falco, I think the mid-tier matchups with Falco and Marth are about equal, which to me makes what you said not apply when debating Marth vs. Falco for 3rd spot.
As for what Shaya said, depending on how many people start playing Diddy Kong or Ice Climbers, it may prove more important to fare at an even level against Diddy Kong than Ice Climbers/Pikachu/anything else Marth can do better than Falco.
Also, I had a question.. on the match-up index, it says that Marth has a +1 vs. Snake. If that's true, or rather, if Marth can play Snake even slightly better than Falco can, that might also come into play, possibly as much as the Diddy situation.