Vulpix: 6/10
To be honest, Vulpix was more of a liability than anything else. Of course, it is what allowed Bellsprout to sweep, but it offered no significant defensive or offensive presence. It could take one STAB hit from basically anything, and return a decently hard hit, but it needed to avoid knock off and super effective hits as much as possible. I would expect that a Modest Choice Scarf variant could do well on it's own, but with a timid heat rock set, Vulpix was just a little bit short on speed, bulk, and power. However, it gets a 6 instead of a 5, just because it was great at putting Misdreavus, Meditite, and a number of other mons in OHKO range for Bellsprout.
Bellsprout: 8/10
Bellsprout was a very threatening sweeper with Growth and Weather Ball, which is what makes it more useful as an all out sweeper than either Bulbasaur or Oddish. Bellsprout has just enough bulk to take a Sucker Punch from Bisharp, and has enough power to blast through walls like Spritzee and Porygon. The biggest problem with Bellsprout though, is that it is hugely vulnerable to Fletchling, and that it needs a boost in order to OHKO a lot of threats, and its not always easy to get set up. The bottom line is that Bellsprout and the other chlorophyll users just can't fill Tangela's big red clown shoes.
Miscellaneous thoughts: Chinchou pairs up very well with sun teams, and can take the strong flying type attacks that chlorophyll users fear, and it's slow volt switch is great at bringing chlorophyll sweepers back in after OHKO'ing or forcing out flying types.