Vivillon is more likely D rank if that really, there is nothing it can do that something else can do much better. A Bug- and Flying-typing is horrendous, it's hit for super effective damage by Rock, Flying, Electric, and Fire some of the most common offensive types at the moment. Base 89 Speed is painfully slow for something this frail. A Timid Hurricane, there is no way this thing can use a Modest nature effectively as it is already outsped by base 100s, doesn't even guarantee an OHKO against a 0 / 0 Venusuar. I do not think a Choice Scarf is really the best idea, Choice Scarf Sleep powder is the only use I can think for it. Salamence the most common Choice Scarf Pokemon can OHKO with a Timid Fire Blast. For Vivillon to function at all the team needs to be built specifically for it, not something you want from a "support" Pokemon. Rotom-Heat is definitely A rank, it can take on Grass- and Steel-types that Rotom-Wash can't beat like Ferrothorn, Gourgiest, and even Aegislash really. It can get away with running more a lot more physical bulk, quite needingly to allow it to survive multiple Rock Slides. It is also able to run a lot of Special Attack to OHKO Aegislash in Shield Forme.