As I said, Victreebel does reasonably well against Rain
feel free to correct me if you are wrong but does'nt Victreebel need sun up to successfully handle rain? With 80/65/60 defences I doubt that it can handle rain as well as you claim. Sure it has Sucker Punch but with its poor defensive stats then its struggling to switch in (especially when pretty much any Rain abuser has a move that can OHKO it or at least cripple the blasted thing). If you are running a weather inducer just so you can check and beat rain easier (while still doing well vs other non rain teams) then something is wrong.
I am aware that Sun Teams can win vs some Rain teams but in all seriousness if we have to run weather inducers to have a chance vs other teams then I believe its over-centralisation. Yes I myself have managed to run a team without a weather inducer (therefore yes I have a few "specialised pokemon" that still stacks up well vs Rain however it loses its viability against other dangerous threats in the Gen 5 Metagame. I think that Rain forces you to devote a few slots on your team just to check it if you don't run weather.
EDIT
Please tell me, how is your "carrying 3 counters to rain" any different from 4th Gens idea of carrying checks to most dangerous pokemon which most certainly took up at least three spots.
Because if you are running 3 Counters to Rain them you are limiting your flexability to other, non rain teams. In Gen 4 Scarf Jirachi was a decent check to top ranking pokemon. However its much harder to do something like this vs rain since they hit so hard and are almost impossiable to revenge kill.