The Samus is easier than Pikachu thing is at least a relevant point because it means that Samus puts less stress on the user. Thus in clutch moments, you are more likely to pull through with Samus than Pikachu when you factor in nerves and the possibility that the player will not bring their best execution to a tournament on a particular day.
In some ways, Samus has a lot of potential too. People have not even begun to scratch the surface of Samus's SH ff missile tech or her SWD in critical situations. Bomb pressure on shield has still not been explored much either.
My point still stands. Samus has less tools so it doesn't matter how easy they are to execute. Especially at high and top level play where the competitors are far more consistent. Marth has easier execution than Fox but that doesn't mean Marth is better in the Falcon MU or Puff MU or Sheik MU. He doesn't have as powerful of options.
Of the things you have listed, I think bomb pressure is the only one with merit but SH ff missile is still slow and its really hard to see a game changing application of SWD.
Pikachu inarguably has more potential since only one player has developed him at high/top level and it seems unlikely a character can be solved from one perspective. Stuff like dthrow tech chasing, and pivot options (especially approaching pivot uair which gives him a disjointed approach) seem far more practical and haven't been implement yet.
I'm pretty sure Plup still uses Samus for spacies. The MU is better than Sheik and Pika vs spacies.
Er, no. The only MU Plup seems to switch back to Samus for is ICs which Samus is absolutely better at than Sheik.
Plup was having controller issues and probably opted for Samus to compensate (since Leffen isn't good at the MU) at Evo 2015. This is basically the only instance where he switched back. The day before he beat Mango with Sheik and went Sheik vs Mango, Leffen, Westballz, Zhu, etc at CEO... so I have no idea where you are getting your conclusion from.
Whether it be Sheik's ledge options, non tether grab and amazing grab follow ups, stellar edge guards/gimp game, higher resistance to vertical KOs, etc. Sheik is absolutely superior in the Fox/Falco MU.
While Samus's high tier Fox/Falco MUs are disproportionately better than her other top tier MUs, they definitely aren't as good as Marth, Sheik, and probably Peach when its all said and done. I think people are just **** riding Samus since Leffen lost a couple times. People shouldn't forget Hax utterly dominated Plup at BH4 or that Alex19 beat Hugs like a week before [after?] the latter beat Leffen; its a completely different look when the player knows the MU.
IMO, Pikachu has the better tools on paper and the data to back it up. It feels more or less assured that he has the strongest Fox/Falco MUs in mid tier.