Besides this, Chikorita's performance considering what it costs to use and how it's built doesn't sound like B rank to me (which I consider to be "workhorse" at least, unexciting but fully usable). It has poor match ups against the majority of Gyms (Falkner, Bugsy, Morty, Jasmine, Pryce, Claire, Erika, Janine, Blaine), the majority of Team Rocket's Poison types (and even their secondaries are commonly Flying or the odd Fire type), the Elite Four (Lance, Koga, Karen packs a lot of Poisons, and Will has Xatus, Exeggutor, and Jynx), and doesn't add much for Red (loses to Charizard and Venusaur while only being advantageous against Blastoise). Major Battle viability is very bad for it on an offensive and defensive front with Pure Grass Typing.
Its movepool is downright terrible. It basically gets Grass and Normal coverage, with only the highly competed for EQ TM to give it another offensive option, and it's essentially unable to scratch the majority of Steel types, Flying types, or generally its STAB resistors because of this. Razor Leaf is also its only STAB move bar the only-slightly-stronger Giga Drain, which is a far cry from Feraligatr's Surf access, or even Typhlosion's Fire Blast/Fire Punch (depending on if you hit the Game Corner or just the Store) for even worse coverage. It's built more for utility and status effects in terms of stats and movepool, but this essentially comes at the cost of two higher ranked attackers and means it either wins by war of attrition or is best suited to catching other things, at which point you could just choose the other starters to have said efficient things from the outset. Typholsion can at least learn Thunderpunch to cover the odd Water type.
Pryce? Meganium is the only one that hits everything he has with STAB Super Effective damage. In return, the strongest move you'll take is Aurora Beam from a far underleveled Dewgong (which is not really a powerhouse). Meganium murders Pryce, not the other way around. It's perfectly workable with Jasmine also and Clair's Kingdra - one of the hardest battles of the game.
C'mon, the Rocket's Poison? They are always like 10 levels underleveled. The family learns Body Slam naturally, which is, if I must say, an amazing feature, moreso in this game.
Its stats are pretty good. It has decent offensive stats and amazing defenses, with a pretty decent Speed.
It is the worst of the 3 starters, there's no question about that. It has some poor match-ups, no doubts either. But it isn't a deadweight. And, once again, it's not how we rank it, but does it deserve to be ranked equally with the likes of Bellossom and Hoothoot? I don't think so.