I'm more practical theory based and use a great deal of "experience" bias.
I'll look at things in terms of reaction speed, 'pressure' (the average to even top level "self-defeating" that occurs) and then my 6-7 years of pretty dedicated evaluating of tools in every smash game. I've been saying things much longer than 'obvious results in the meta', because I've also been lucky to see these developments outside the tournament realm. I wouldn't be surprised if I've seen more top level Pikachu play than anyone else in this thread (streams that feature all various sorts of great players I seek out that only ever have 5-10 viewers at least gives me this impression, let alone in person training and top players 'nutting out' options).
Anyone who hasn't put themselves through Brawl ICs impact of the meta is usually someone I don't see as truly understanding what the **** is going on. Putting Sheik above Diddy plainly ignores his match up skews, results and a very distinct barrier for players to succeed even if they're winning 65:35 in most game states or better. Sheik is the best character in the game at 0%, at 100% I wouldn't put her as top 5. With a stock lead I'd put her better or second best to Diddy, at stock deficit? She's quite pitiful. Diddy is always top 3 at worst in every match up in these various conditions. If you rate them linearly / as a ratio of time, then Sheik forcing a slow excruciating death definitely puts her as no.1... I guess.
Blaming yourself is fine, but there are limits to your character, if Pika has game breaking abilities to overcome this, then you wouldn't be switching to Diddy or Luigi.
Pikachu hasn't been shown to do a single thing super-noteworthy bar a Day 1 WiiU tournament. I've been using Pikachu since day1 of 3DS and had very high expectations for him and will be happy to be proven wrong.
I would put characters like Falcon and Luigi, despite having obviously weaker neutrals (and less options in disadvantage) as better as Pikachu right now because
their moves are stupid, something we almost all agree on, oh and to top it off there's ACTUAL RESULTS for them too.
Mobility is an amazing part of a character, in this game thus far it's one of the biggest attributes we're looking at. But Pikachu lacks something very distinctive, and that's pokes/spacing tools. Down Tilt does not compensate enough (if that were the case, Marth would be having a much better time against good characters). He uses the shallow design of his frame/size to give him a semblance of one, but it's "fake" and will only continue to have counter-play developed with little to expand on from Pikachu's part. If you already have a punish consistently down for when Pikachu fairs or bairs (yes, yes, grounded Pikachu is the only Pikachu, Macachu~), chances are you're going to destroy them. If you take the strength of Pika's chaining/combos and look at how his tools don't allow him to maintain a dominant positional advantage (unlike Diddy, Sheik, Falcon, Sonic, Rosalina) afterwards, then the pressure the player has dealing with Pikachu diminishes drastically ["oh this could happen, but it's not that debilitating to me or my game plan at all"].