I see where you're going, but he's more like tier 6 I think. Falco might be better than Marth (Marth is my main, Falco is my second). The lasers give Falco a major edge on so many matchups, and chain throw deals with so many others. Marth has viturally no way to deal with projectiles, and can be camped against really hard. Due to the defensive nature of Brawl, this puts Falco a tad above him.
However, Marth is more likely to beat most opponents than R.O.B.. Marth has better approach options, decent defense options (though agreeably not as good defense as R.O.B., due to the lack of a way to deal with ) Worse recovery, but harder to edgeguard. Due to the tipper, and a more usable meteor smash, Marth has better finishers, and he's less predictable than R.O.B.. Despite his negative matchup against R.O.B. himself, he a flexible character, and just much more likely to place a victory.
The problem with Marth is that despite his **** matchups against so many characters, he has a negative match-up against quite a few top characters. Out of the top and high tiers, he loses to Snake, R.O.B. and Falco (possibly his only three bad match-ups in the game, but all top or high tier), and is neutral against D3 and Metaknight (D3 has range, weight, power, and recovery on him, and Metaknight has speed and recovery on him.) He can knock out G&W and Wario, but that's where it ends in the top and high tiers for him. He has a pretty positive match-up against the vast majority of the rest of the roster, but he's not going to place 1 in most tournements because the other really great characters fair well against him (it's tough for me to say that as a Marth main, but talking statically, it's true.)
R.O.B. beats , Marth, Wario, and can beat Snake at times. He's about neutral with D3 and loses to Falco, MK and G&W. Not awesome, but looks a bit better than Marth., due to a better matchup against Snake (perhaps)
Of course, all this data is still subjective and speculative. Game hasn't been out 4 months yet. Just my .02