Roserade is almost never used in Doubles. It’s primarily used as an offensive Spiker in lower-tiered Singles. However, when it is used, Weather Ball is run a decent amount of the time, essentially for the reasons you described. The trouble is that it’s outclassed by Venusaur, which gets Chlorophyll, Growth, and Weather Ball, plus it’s bulkier, so Venusaur is pretty much always superior. In Singles, you’ll want to set up Spikes, not waste a turn with Sunny Day. In Doubles, while it does work, there’s no reason to use Roserade over Venusaur, as there’s almost never a need to set up hazards in Doubles, and Venusaur can take more hits.
Hope I helped!
