The SoCal Pikachu (the name slips my mind, fffffff), beat Mr.E in two sets at an MSM after Evo/Ktar Saga.
Mr.E is particularly fearful of that match up, Pug isn't a huge fan either IIRC.
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While I think the match up has room to grow, going by results and general "theory" (of why things are awkward/difficult for Marth), it is fair to say it's in Pikachu's favour.
Really solid dash to shield game against Marth, the right type of burst options, can trade favourably with recoveries and can make it very difficult for Marth to get back into neutral.
Ideally, Marth wouldn't lose, but until solid punishes for QAC are forged (I suggested to Mr.E the use of reverse up tilt / up air due to their large arcing space and duration rather than nair) and not actually being one of the few characters Pika can reliably set up and continue his advantage state on, the current assessment is valid.
P.S. Marth's up-b is 5 frame start up, but doesn't sweetspot the ledge after frame 5 until like frame 12ish IIRC.
Knowing that Marth has to be a certain distance from the ledge vertically to actually not be susceptible to a trade near the ledge or being baited into a KO allows "reactable" types of situations.
Theorycrafting (it's more like mashing buzzwords together than actual craftsmanship though :<) can be so painful to read sometimes.
If you're not entirely certain of something, instead of either skirting around it or proclaiming something as fact, just concede you're not certain in an area... perhaps a third-party will chime in with information that will advance the conversation in a better way.
We're analysts here, not petty folks with anything to gain.
12 frames isn't reactable either. Smash 4 has 6 frames of input lag (or around there anyway) plus however many frames Pika's bair would take to come out assuming you were already at the ideal spot. Even with above average reaction time, you aren't reacting to jack.
I've explained how Marth can mix up and actually counter react to Pika going offstage.
Another thing to keep in mind is even if bair clips Marth, if he was high enough when it happened, he can instantly up B again and still make it back.
I've conceded a while back the matchup is in Pika's favour if top Marths think it, I just don't think it's because of edge guarding alone.
QA should not be a big issue outside of platform heavy stages. It has 15 frames of startup + however long it takes to reach Marth. Not only this but trying to read it doesn't get you punished. If Marth is expecting it and through out a pre-emptive ftilt/fsmash or something, either Pika did it and got hit or did nothing and was too far away to punish.
You put so much emphasis on results, yet don't check results either. You truly are an enigma. Has a Pikachu beaten a Marth recently? No, cause there's no one out there actually using Pikachu to begin with. And I brought up how edge guarding works for every character in the game, not specifically Pikachu. If I were to mention Pikachu's edge guarding, I would name one of his moves. Such as bair. You don't even have to trade with it, you can hit Marth from behind the disjoint and get him that way. Or you can throw a Tjolt where he's going to go. Or go off and dair him where he's trying to position himself to up b.
His recovery is predictable. You do not have to react to it. Predicting something doesn't have anything to do with luck, it has to do with noticing your opponents patterns. As has been already said, Marth is always going low. You know where he's going to be. And you're still thinking about edge guarding as if you are right next to the stage. That isn't always the case. You don't even have to go off stage, ledge trumping is a thing too.
Not only that, but you're severely underrating Pikachu. He isn't Edge Guarding: The Character. He has a fantastic, practically lagless up special that is great on platforms and acts as an approach and can lead into up tilt or a grab if you shield which starts his combos. You talk about reacting to things all the time, you're not reacting to that up special. The only reason you would ever be able shield that move is if you knew it was already coming. He has a solid projectile that forces approaches and also allows him to approach. The entire Marth v Pikachu MU is literally just both characters trying to play as lame as possible.
Ledge trumping doesn't work if they buffer options. Also it's not particularly good with Pikachu anyway until extremely high percents. Dair and nair are too weak and bair won't directly kill either.
As for Pika's up B, as mentioned above it's 15 frames on startup + the second iteration + the time it takes to reach you. All of this combined gives you enough time at the very least to block. And as I explained above, trying to hard read the move isn't a bad idea either, Pika will likely be too far away to do anything about it even if you are wrong. Watch notable Pika's in action and on most stages you'll notice they don't use up B much in neutral. It's a gimmick more than a solid option. It only seems amazing in low level play.
Once again in practice, Mario and Marth rarely get gimped. You know they are going low but don't know the exact moment they are about to up B, slight changes in timing mess up your edge guard and good players don't recover the exact same way every time. They can react to what you are about to do and do an early up B for instance.