Another thought that's just slipped my mind (again, possibly concerning Flower Gift) We keep saying that we don't want CAP5 to have absurd special bulk... but having a look at the things we want to threaten us, none of them solely use special attacks, and those that do either have Bug or Fire STAB. I've got a list of things below that still threaten CAP5 if we give it, say, Blissey level bulk while Flower Gift is active and fully invested, while leaving it with modest physical bulk.
Things that still threaten us
- Scizor, lol
- Ferrothorn, can probably 2HKO with Gyro Ball
- Dragonite, could either set up on us or kill with Outrage
- Jirachi, any set with Fire Punch or U-Turn
- Heatran, still 2HKOs with Balloon Fire Blast
- Breloom, can Mach Punch us to death
- Terrakion, if it can switch in safely
- Keldeo, Secret Sword bypasses SpD
- Salamence, slightly worse than Dragonite
- Volcarona, always 2HKOs with Bug Buzz and can set up
- Skarmory, walls and KOs with Brave Bird
- Mamoswine, if it can switch in safely
- Infernape, hits hard with physical STABs, U-Turn
- Cloyster, can still hit hard
- Lucario, lol
- Kyurem-B, lol
- Hydreigon, if it has Superpower
That's a pretty big list, and by no means is it exhaustive, and doesn't it look very, very close to our current threat list? Yes Ninetales isn't on there, but bleh, it can still Wisp CAP. So if you're concerned about massive special bulk removing threats from our threat list... that's not the case. And massive special bulk sure makes checking Latios a hell of a lot easier... Even with out Flower Gift, an uninvested 69HP / 180 SpD CAP5 can take a Specs Latios Draco Meteor (or two Scarf Meteors) and follow it up with Life Orb Crunch without dying, meaning it's certainly not useless in Rain, while still getting much better in Sun. Combined with my previous post about Flower Gift, I'm seeing fewer and fewer reasons to think Flower Gift would be broken, as long as we're careful with the Attack stat. Looking back at the criteria I answered from my earlier point, Flower Gift also satisifies points 1) 2) and 3), sorta satisifying point 4) and not being affected by point 5) So at this stage it's either Flower Gift
for the primary ability imo, as they are more constrictive on stats than the also awesome Harvest.
EDIT: To the below, that's exactly my point. We can give this thing absurd special bulk and it'll still be threatened by the things we want it to be threatened by, as discussed earlier. This is a good thing, as it means CAP can wall latios all day with blissey level bulk while still being threatened by a lot of Fire, Bug, and Ice types.