I'm not sure what you mean. I never forfeited control of the situation; it's not like I ran to the other side of the stage? I was actually fishing for a desperate jump or roll as he was in a bad position (which I maintained). He whiffed a spot dodge and jab; I didn't trust myself to react quick enough to those considering he could have double jabbed me and interrupted me with the second jab. He did end up rolling which is what I was looking for. What would you have suggested instead? Dtilt -> run up grab? Dtilt -> dtilt again?
Sit at that range and react. You could literally just stand there (imo best option right there). You could Dtilt again. You could walk forward a little and back up w WD back. Even though I think it's a low % success rate play, if you wanna DD there you've gotta tighten your DD more or change the rhythm, you got lucky that he messed up even though you baited the roll. The point is that you had him in a position where he was disadvantaged but you actively forfeited control by dashing away after the dtilt AND doing a very long, relatively monotone DD. In another way: you had guaranteed damage/strong pressure and you decided to pretend it wasn't guaranteed/he had more control than he actually did.
Looking at it again you actually dtilted his shield. Why are you moving at all? You don't have to move, HE DOES, and the beauty of it is that you're at a nice range where you have enough time to respond to him despite how slow some of Marth's moves are.
After the nair I hit him with, I was still around center stage and he might have thought it safe to drop straight to the ledge (which people like to do in order to save their double jump). In this case he opted to double jump which is the proper response to me trying to hit him before he can grab the ledge; it was a hasty move but not necessarily without a reason and it did cover an area of the rock-paper-scissors game that goes on in playing. If I opted to fish for his double jump, he could have dropped to the ledge and I would lose some of my advantage (but in this case he won the RPS obviously).
So this is a really good example of why Umbreon advocates structuring your learning dichotomously rather than using a gradient; ie there's only a right decision, and everything else is wrong (rather than this decision is more right than the other). This decision DOES cover one of his possible options in that specific situation, this is true. And it's plausible that he would fast fall to the ledge. But you have to ask yourself, is it LIKELY that he should do so? Well, it's as you said: one of three available options. But consider that it's very risky for him to do so given the threat of coming in on Marth at that angle. You have a ton of different options that would make him **** his pants if he even tried it. We could chalk this up to inexperience, but that removes part of the teachable element of this situation (which is what I'll talk about in my next paragraph).
So OK. For whatever reason, you choose to throw out fsmash; now WHY is it right? You say that the fsmash is a high reward option that can be beat by double jump. Well, what if I tell you that you can just wavedash or hop back and you will be able to reactively cover all of his options and he cannot defeat your overwhelming advantage with any options? This is the proper way to evaluate situations. How do I place myself in as many advantageous situations as possible? Until you master this ability, only then should you focus on "exceptional" situations that require more creative thinking or have some sort of strange contingent element. You will vastly improve your consistency of play by this method.
Yeah you're right that I probably need to be looking for grabs more, but I find it disconcerting that so many people think that swinging is bad in this matchup. Swinging is necessary on so many levels and are just as important as grabs are IMO (yes, in the neutral game). The threat of swinging is what scares opponents into shield which is what opens up grab opportunities... but of course this is a really basic principle. You had a good example of where grab more was appropriate earlier though (with the fairs that I do).
It's as you said: the threat of swinging is what's important. Not the swinging itself. There's very few situations where you need to actualize the threat of swinging by doing an attack w the sword because of how "slow" Marth's moves are.
Can you elaborate on this? I'm not sure I'm understanding how being thrown at higher percents is a free escape and why it's any better than being fthrown at lower percents (proper DI should keep you from getting combo'd off fthrow at the very least). And I'm definitely not understanding what you mean with dthrow.
Fthrow at higher percents at the edge = tons of variables (DI/drift, does opponent have jump or not, also opponent has the option of resetting the situation by grabbing the ledge)
Dthrow at higher percents = less variables (DI, then it's an okizeme situation where he can only land normal + do getup options or do ukemi (tech) + do that set of getup options)
It's a % success rate game.