Venu gets Sleep Powder to make its lategame easier, and Swords Dance should be ideal for it. That said, I would be okay with moving it down to B, partially because its route performance is worse than that of the other starters as well. Having great Gym match-ups early doesn't quite make up for its mediocricy later.Also, Venusaur sucks and I'm pretty sure it's gonna easily drop to B in my opinion, unless I'm missing something in using it. It falls off HARD after Lt. Surge and never really recovers. It feels like it 3HKOs every Grass resist with Body Slam, and even in matchups you hit neutrally like Sabrina, they have high Special or SE moves. Just...not very good, though I haven't tried Swords Dance, Double-Edge or Hyper Beam, admittedly. And even then, I feel like they are simply a Band-Aid over Bulbasaur's problems rather than Bulbasaur being a good mon in itself. I want to be nice and say A, but I don't think I can in full confidence, at least right now. Sorry Bulbasaur.
If any of you guys have different Bulbasaur experiences, let me know. Maybe I'm doing something wrong.
Magikarp can also go to B, the pre-evolution period sucks not only for it, but also for the rest of the team; and it's amplified by the Slow EXP group.
Speaking of Magikarp: I think we can bump Dratini down to D. While it has a good movepool and nice typing, it'll require TMs and spend its pre-E4 time as Dragonair, and Dragonair is a fairly weak Pokémon at that point in the game where most other Pokémon in your team are fully evolved or close to it. Its E4 matchups are less than stellar as well with both Lorelei and Agatha causing a lot of trouble for Dragonite.