If you're basing your opinion on your personal experience online, then sure, Pichu is not even high tier. We have layered metas where the lower the skill level goes, the lower Pichu would be on that hypothetical tier list. Pichu does not make a bad player better. He makes bad players worse and only shines in the right hands. He's also severely nerfed in online play by lag.
If you're talking about super major top 8 meta, then he is clearly one of the best characters in the entire game, if not the single best. He has a zero to death infinite that works on almost everybody and its just a matter of time before we see it mastered. He has incredible combo potential, incredible kill power, one of the best recoveries in the game to enable off stage play, insane frame data and out of shield play, one of the best projectiles in the game, and a tiny hurt box. All of this is counter balanced by dying early and his range, but he has all of the tools and more to be light and small and still dominate most matchups. He has the means to exploit the weakness of virtually every other character in the game. Being small with elite frame data, recovery, and massive kill power is like checking all of the boxes to be S tier in a smash game. See SSB. SSBM, SSBB, and Tr4Sh tier lists.