M2k made me look at it this way. You can dash attack a marth, or you can grab. You have 2 main options, and he has two main options (attack/shield). That reduces your chances of succeeding to about 50 percent. If he attacks, you dash attack, if he shields, you grab. It seems really simple, but there's a genius to it.
I guess this is where the outplaying part comes in, and where I took some freedom with m2k's strategy. Your goal is to go from a 50% success rate to about 90% with successful baiting and reading. You can bait out the shield, you can push in just enough to bait an attack, then come down with a dash attack. Be constantly moving. Naturally, you'd have to have your follow ups down.
Marth has no defensive Fair game if you fight him this way. Why would he SH fair defensively at a samus who isn't attempting to move in. Samus should only be baiting.
Marth is a bit limited, and with this strategy you get to exploit those limitations. The point is to control the middle ground, when you give it up, you ride the platforms to the other side, and repeat.
I really have had zero problems with marth since, and it's starting to feel like a "gimme" matchup in brackets now. I don't know if I've changed my opinion on the matchup yet. If it's just me outplaying them, then the marths will catch up. If it really is an inherent advantage within Samus, then I'll be able to maintain this success for a long time much like I have vs Falco/Fox.