Scrappy has use. Just not any notable use.I see absolutely no use for Scrappy on CAP8.
Again, Forecast is just another rather gimicky ability Game Freak made because they thought it would be interesting to implement.It's not true that no good can come out of Forecast. Rain Dance and Sunny Day teams are not completely horrible. The only downside I can see to a weather-based CAP is that it has nothing good come out of Sandstorm. If it got a defensive boost from it and worked in that weather as it does in the others, it would be just as competitively viable. The question is can it survive even in this sand-filled metagame? Pyroak can benefit from Sun, Arghonaut from rain and Syclant from Ice, so it's not like the CAPs can't have any synergy with Forecast on a Pokemon.
Real Pokemon have a LOT more basis on flavor and such than we're really going for at CAP.
Of course, most abilities have SOME sort of advantage to them, and Forecast can be a help in some case, but it's really just completely out of place on it. It could much rather use something else with more notability. Forecast is too out of place to really be used.
It's there mainly for Castform, just because.