It's funny because I, like many others, feel that the over-milking of Charizard is frustrating, yet I don't feel that way about Pikachu and yet Pikachu also gets a Gigantimax form, 2 Z-Moves, like 20 different forms (hats, X and Y costumes, Let's Go Partner, etc.), an exclusive Item, an exclusive move, and several staring roles in different games.
I think it's in part because Pikachu is the mascot and so a lot of this favoritism is something to expect, whereas with Charizard he's clearly been favored over the other Pokemon he's supposed to share a spotlight with equally: Venusaur and Blastoise. I would also say it's influenced by the fact that, despite GameFreak having complete control over the game's design, none of their Pikachu favoritism has done anything but make him anything more than an extremely gimmicky pick barely worth a slot even in the lowest of tiers.
None of the alternate Pikachu forms do anything to fix Pikachu's problems
Both Z-Moves require you drop the Light Ball which is a blatantly worse choice offensively
Volt Tackle's absurd recoil was entirely unnecessary. Even Raichu is nothing spectacular, so if Volt Tackle was just a move that had no secondary effect it would be far more passable and still wouldn't actually make Pikachu or Raichu too much better competitively. They certainly wouldn't be OP.
I suppose you can have Lightball on Gigantimax Pikachu, but I feel like you'd still go farther with basically any other Pokemon (I also don't acknowledge Gigamax's and Gigantimax's existence personally so I'm not the best judge).
I don't really see a problem in having a mascot Pokemon. I find it a bigger problem that the mascot's so completely awful in the games themselves. Ironically, that story about Clefairy being considered for the mascot over Pikachu would actually have given us a much better mascot in gameplay. Both Clefairy and Clefable are really useful: Clefairy in doubles and Clefable in singles.
