Roserade

Great League: 2 / 5

Roserade's offensively-oriented stat-spread leaves it quite vulnerable due to the CP cap of Great League. The addition of Weather Ball Fire isn't particularly unique, as Cherrim (Sunshine Form) sports a very similar moveset. Between the two, Roserade offers more consistent Grass-type coverage thanks to Grass Knot demanding less energy than Cherrim's Solar Beam, and Roserade is more flexible with additional Poison-type coverage options, but Roserade is more frail and has below average bulk compared to the meta. A Grass/Poison typing is generally considered more safer than pure Grass typing, but this doesn't solve Roserade's bulk problem. 

Ultra League: 2 / 5

As a Grass-type, access to Weather Ball Fire is quite valuable against other Grass-types, in addition to common Steel Pokemon in this league. Unfortunately Roserade's fragility is its primary setback, with losses outside of 2-shield fights against level 50 Abomasnow despite the latter's double weakness to Fire-type attacks. Roserade's role as a Grass-type may be difficult against certain Water-types with either counter coverage or secondary typings to neutralize their weakness to Grass-type attacks, while its Poison-type coverage isn't necessary to beat Togekiss unless both shields are used. 

Master League: 0 / 5

Roserade lacks stats, in particular bulk stats, to compete well in Master League. Due to the stat differences in Master League compared to Ultra, Roserade can't beat Togekiss in any even-shielding scenario without Poison-type coverage, which means sacrificing something else in its moveset choices. The fast moveset of Bullet Seed + Weather Ball Fire is needed to challenge Metagross, while Poison Jab movesets are too slow to keep up with Swampert should the latter successfully bait a shield with Hydro Cannon. Overall the difficulties and consistency problems with Roserade makes it discouraging to use effectively, and other popular picks might be a better choice.