You can't just make the argument that Pikachu has the ability to turn bad Pichu matchups into even just from something as simple as Quick Attack properties and Self-damage.
I didn't, I also mentioned range, which is
huge.
You can't attribute Pichu's superior results over Pikachu with "the character isn't running into bad matchups."
Oh, and why is that? If Pichu wins every matchup but, say, 7, and Pichu mains almost never seem to run into those MUs (or switch to a secondary if they do), then we should keep that in mind when evaluating Pichu's tournament results. Even VoiD used Wolf to deal with Shuton's Olimar (he got 2-stocked with Pichu and then switched to Wolf and won the set).
If anything, tournament results have shown us that Pichu is more solo viable than Pikachu. Also it's not really a tossup on which character is better at the moment; Pichu is blatantly better.
Pichu is easier and arguably more fun to play than Pikachu, and some of the things Pikachu does better than Pichu can be pretty boring (Pikachu is better at playing campy, for instance, but most players, I would imagine, don't like playing campy). It's no surprise that a character with more players get more results, especially since Pikachu is harder to play. It's also notable that ESAM seems to stick with Pikachu more often while Pichu main often seem to have a secondary to fall back on.
That brings up another point for discussion: Should tier lists be based only on solo viability or on the character's value as a whole? Some characters are great secondaries or do great with a secondary, while others are solid overall but don't have the same strengths. I believe that tier lists should determine
solo viability, so characters with great strengths and notable weaknesses might be lower on a tier list than characters with a more overall strength/weakness spread. With that in mind, it's possible that if we had an equal amount of Pikachu/Pichu players at top level, and everyone solo mained, Pikachu would do better.
That's one of the issues with relying on results: Some players
don't solo main. VoiD doesn't, NAKAT doesn't, Captain L doesn't, while with Pikachu, while ESAM has been talking about using Yoshi, he's been relying on his Pikachu to take most sets. This means that players can switch characters to avoid bad MUs and thus make the character appear better than it really is. It's possible, and quite plausible, that Pikachu is more well-rounded than Pikachu and has fewer bad MUs overall. It's also possible, and quite likely, that Pichu players who also have a secondary can make up for this deficit by switching to the secondary.
Now, am I saying that Pikachu for sure is better as a solo character than Pichu? No, I don't know whether he is or not. I'm saying it's possible, and more than a bit probable. The argument can be had, and it's not obvious that Pichu is a better solo main than Pikachu (though Pichu + secondary being better than Pikachu + secondary is a different story, and I won't contest that Pichu is most likely better in that scenario).