Lmao, I'm not against your opinion, but I do think Pikachu isn't that overrated, well it's normal for me since he's the mascot of the franchise.
I agree. I don't feel like people say "Oh my god, Pikachu is the strongest Pokemon in the world!" Sure, you see him everywhere, but that's because he's the mascot, and a cute Pokemon. If you're going to say that Pikachu is overrated because you see him on Pokemon merchandise, then you better be saying that Koffing, Geodude, Zubat, Machop, and Goldeen are overrated, since they statistically are the most used Pokemon in game (78, 73, 71, 60, 51 instances, respectively).
Charizard, everyone thinks hes really good cause of his appearence when venusaur, who is ugly, has way better stats then him.
Actually, you're wrong. All the starters have 425 base stat total. (HP/ATK/DEF/SPD/SPE) Venusaur has 80/82/83/80/100, Charizard has 78/84/78/100/85, and Blastoise has 79/83/100/78/85. Though Venusaur has a whopping 100 in the Special category, the only special type move he can learn is Grass, which can be easily countered by switching to a resistant Pokemon. Movewise (direct damage moves exclusive), Charizard gets access to Normal, Fire, Flying (Yellow), Ground, and Fighting, while Venusaur just has Normal and Grass. Even Blastoise, which you failed to mention, has Normal, Water, Ice, Ground, and Fighting. So statistically, I'd say of the three, Venusaur is the worse, having only one Special type to use. Charizard doesn't have nearly as much special, but he also only has one special type. He has higher attack, and he has more Attack based type moves.