from A- > B+
Honestly, after reading the arguments about Roserade I want to argue that it should drop a rank. Roserade's most common role in the tier is as a hazard layer/offensive pivot that can deal with bulky waters. However, Roserade suffers from a multitude of things that happened with the onset of the ORAS metagame.
Hazard Setter:
First, we saw the loss of the most prominent spinblocker in the tier, Sableye. This is a problem for every hazard setter, but especially so for hazards that take more than one turn to fully set up (spikes, tspikes). Spinning isn't the primary way to remove hazards in this metagame though. Every common defogger in the tier beats Roserade 1vs1. Crobat outspeeds and OHKOs, Aero outspeeds and OHKOs, Gligar defogs for free as it fears nothing from Roserade, Empoleon does the same. So the point of this whole argument here is that it has no way to keep its hazards on the field even though they take more than one turn to set up.
Offensive Pivot:
Roserade really is not the greatest offensive pivot either. When looking at the Pokémon in the A rank on the viability rankings, Roserade can safely switch in and force out only a handful. Going further down the list reveals the Fairy-types who arguably preserve Roserade's niche in the meta. However, Poison resists are not hard to come by and almost every team has one or more very solid switch ins to Rose regardless of what it can come in on for free. Moreso, Fairies are definitely on the decline. Even so, its horrid defense stat prevents it from even coming in for free against Swampert who deals roughly 60% even without offensive investment. Roserade also faces stiff competition from the likes of Shaymin and Celebi who can provide similar amounts of team support with Baton Pass and Healing Wish while having much better overall bulk.
In summation, Roserade, while by no means a bad pokemon in the metagame, has suffered from the same fate that many hazard layers have faced. Being beat by every common defogger in conjunction with the tiers lack of a reliable spin blocker limit the utility provided a Spikes or Toxic Spikes set. The offensive pivot fails to come in safely vs many top tier threats and its speed tier falls short of what is normally required for an offensive mon at the moment. Roserade is still a viable choice but falls far from the A- benchmark for me.
Roserade to B+