PKThunder's answer is good, but I want to elaborate on the topic more.
Like PKThunder said, Petal Dance isn't really good because it locks you into one move, and moves that lock you usually aren't that good. Set-up Sweepers can take advantage to set-up and well, sweep. Also, Leafstorm is usally better.
I decided to ask the RU room on how Roserade is there. Galarian Birds OU answered saying it checks Electric types like Raikou and it sets up Spikes. I decided to ask about Offensive Roserade, and yourwelcomethank answered saying it's good and gave me this set:
Roserade @ Heavy-Duty Boots
Ability: Natural Cure
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Giga Drain / Leaf Storm / Grass Knot
- Sludge Bomb
- Spikes / Shadow Ball
- Synthesis / Sleep Powder
As you can see, Giga Drain, Leaf Storm, and Grass Knot are the choices here. An explanation for the choices was given in this Roserade analysis, and while this set is a bit different from the Smogon one, it still explains the choices.
Giga Drain keeps Roserade healthy without pressuring it to constantly use Synthesis. On the other hand, Leaf Storm pressures checks such as Metagross and Stakataka with Spikes up while also OHKOing offensive threats such as Xurkitree and Mienshao with Spikes on the field.
Giga Drain provides healing while Leaf Storm hits hard against things like Metagross switching in. You wouldn't want them bulky steels setting up on you while you are choiced into Petal Dance with no recovery. I also asked if it has a niche in other tiers, and it has a little niche in UU being able to set up spikes, but other than that it sucks there.
I've been talking about other tiers, but now it's time to cover AG. In AG, Offensive Roserade... sucks. bad. It's outclassed and destroyed by the many Ubers and Legends that make their home in AG. It won't last long, and shouldn't be used. There isn't a reason to use Roserade in AG or run Petal Dance on it anywhere. Hope this helps.
