Characters like Lucina and Palu definitely beat Pika because they have hitboxes to shut down tjolt pressure (Fair, Bair) that Pika can't hope to beat, as well as the ability to antiair him more or less for free. A lot of people respect tjolt (and Pika's aerials) more than they actually need to imo.
But nobody focuses on that part of the matchup for some reason.
I agree with the spirit of your post, but I don't think this is true, because that part of the matchup only happens when you're only learning the matchup for the first time. You don't see ESAM using tjolt against those characters because he already knows that they can swat it away. Once you start swatting tjolt away, Pikachu's gameplan has to change.
Pikachu's yomi layers in the
matchup are kind of like this. At first, he's going to try to tjolt you and air-to-air you when you jump to beat it--if you clank with tjolt with an aerial, you're frozen for a bit during which Pikachu can weave around your hurtbox and hit you where you're not striking. Palutena pulls back during her f-air but Pika has the air acceleration to aim at her head, for example. If Palu starts fading back her f-airs, this stops working, so Pikachu switches tactics--since she's not gaining ground while f-airing, he can dash in and shield. Now he has access to some very fast OOS options (f3 nair, f4 bair) which lead to combo routes, and Palutena doesn't have any fast options besides dash attack and standing grab. She can't use short hop aerials as neutral mainstays because he's so short that the timing becomes trivial to parry.
Nairo thinks Pikachu is Palutena's worst matchup. He says that the Inkling matchup is -2, and the Pikachu matchup is even slightly worse than that. Now, I know I just got done saying that people overrate how well Pikachu does against their character, but this isn't true in Nairo's case. In Smash 4, everyone believed that ZSS lost to Pikachu, but Nairo was saying that she won, or that it was even at worst--Nairo is not the kind of person to let his emotions or losses dictate his view on a matchup (he lost to Kola recently and got taken to game 5 but still thinks the Roy matchup is even despite his brother/coach trying to convince him otherwise).
I think the matchup is actually really bad for Palutena on paper and in practice. The thing is, Palutena doesn't have any tools in disadvantage that Pikachu needs to worry about. Up close, she can't respond to mashing pressure since he mashes too low to the ground for her OOS options to matter. Whiffing grab is too punishing for her in this MU because Pika can edgeguard Warp.
is another one that I think Pikachu definitely beats or at least goes even with, mainly because of Quick Attack. ESAM theorycrafted a long time ago that because of Lucina's lack of burst range, you could just Quick Attack every landing on reaction to punish it. I didn't believe it, because I didn't think that the frame data was there to support it--but then you saw him do it against MKLeo's Lucina and Marth. ESAM's one of the only players to ever take down MKLeo's Lucina in bracket (and this was an elimination set, too, in Losers). Zackray also went Lucina against ESAM and met with the same fate. Lucina doesn't have a good enough disadvantage state against Pika combos.
Both Palutena and Lucina do really well against Pikachu's opening strategy, but as you peel back the layers of and get to his other tactics, they fall apart and run out of answers.
What Ness, Game and Watch, and Mario all share is this:
1) they beat tjolt cleanly, no need to trade with it, since they can reflect/absorb it
2) they have lingering hitboxes that prevent easy whiff punishes
3) they get out of disadvantage quickly with big aerials
4) they have options up close when Pika is approaching on the ground
5) they have great grab games off of low-to-the-ground grabs
6) they are short
7) they have free answers to quick attack when Pikachu uses it offstage to recover (FLUDD, Chef, PK Thunder).
8) they are hard to kill
Matchups that I think Pikachu loses:
as a starter. She has the movement to avoid getting trapped up close, and also has the options to contest him if it does happen (f4 up-b OOS is scary, jab is f1). She has z-air and side-b to go through tjolt without actually having to extend her hurtbox far enough forward for Pikachu to hit her, and both her aerial drift and jump height are huge so she can do the fadeback thing like Palu can, only ZSS can do it out of a full hop or double jump too.
Pikachu's airspeed is actually pretty mediocre, but in matchups like v. Palutena he doesn't feel it because Palutena has about the same speed. But in this matchup he definitely feels it. He can't land using Quick Attack because ZSS can burst so fast that she's only ever one initial dash or flip jump away from covering the landing position and possibly killing him at 60, and he gets edgeguarded, something that he's definitely not used to castwide.
Finally, her disadvantage is pretty good in this matchup, again because Pika doesn't have the air speed to consistently catch flip kick out of a bad situation. She does get edgeguarded a bit harder here than in most other matchups though, and Pika can ledgetrap her pretty well.
is another matchup that I think Pikachu loses. Wolf can play the same type of style Lucina can, with a reflector to boot! When Pikachu switches to second-level tactics and approaches on the ground, Wolf has dash attack and also a transcendent blaster to deal, unlike Lucina who doesn't have the midrange burst. Wolf being a fastfaller also means that it's much harder for Pikachu to punish his landings, so Wolf has all the things that Pikachu hates about Lucina but several neutral options that cover her weaknesses.
Wolf's n-air is a huge lingering hitbox that makes it hard for Pikachu to always catch Wolf's landings, and Wolf's air speed is actually pretty great (1.281). Finally, even though Pikachu edgeguards Wolf pretty well, and doesn't get ledgetrapped that hard due to Quick Attack, Wolf has way more reward than other characters in the MU, and doesn't really mind spacing moves low to the ground (f-tilt, d-tilt, dash grab, grab, low f-air, n-air).
is up next, mainly because of Charizard. Charizard doesn't care about Pika combos because he comes out at percents where he's no longer getting combo'd, and so instead of just juggling a heavy, Pikachu has to look to take a stock off of one. This is true of every character in the Charizard matchup, but some characters have easy confirms on Charizard, or have easy ways to get in and bully him, or can just react to whatever Charizard tries to set up at a distance, or can camp him. But Pikachu can't do most of these things. He can tjolt, but tjolt isn't leading to kills. Charizard outranges him, and is very fast on the ground, and has access to some really broken OOS options that cover both sides of his hurtbox (f5 up-smash) that can strip Pikachu of a stock. If Charizard stilll had Rock Smash this would be a -3 matchup, but it's still really hard regardless. As Pikachu in this matchup you're looking to kill Ivysaur or Squirtle before they can switch to Charizard, because Charizard is just a nightmare matchup.
I also think that Pikachu loses to
and
because zonebreaking is actually not easy for him in those matchups and he's vulnerable to a single lingering f-smash read at percents where he's not yet ready to kill but the other character is. Pacman also has some of the best escape tools against Pika combos and Zelda's up-b can eviscerate him for making small spacing mistakes.
So I think overall he has like 6 more losing matchups than is commonly believed, and probably a lot more even than anyone will admit. Luigi's a good call out; that matchup can be hard, though it's easier than Mario just like it was in 4 because of Luigi's overall worse mobility and recovery--the hardest part of the Mario matchup is actually getting the KO on Mario. You'll see ESAM spamming dash attacks against Wizzy because he just doesn't know how to open up Wizzy to get a kill. Against Luigi you don't have to do this since you have a couple of strong vertical tools to end him as he's getting back to the stage (Thunder/d-air).
is in a similar boat.