Ok, so about this whole Suicune thing... The obvious selling point for not boosting it up to A is that Roserade, Shaymin, Raikou, and Zapdos are running around the tier. I've made a list of the 4 main threats Suicune fears, and why they are all threats to be considered.
Roserade- Mauls Suicune with its base 125 Spa, and its Natural Cure allows it to shake off any residual damage from burns that Scald caused.
Shaymin- Seed flare wrecks Suicune, even with a boost. Also, Shaymin can recover any damage taken from Scald burns and Life Orb recoil via Synthesis or Rest. These 2 recovery moves also guarantee that Shaymin will be able to stay alive for Suicune when it comes in late game.
Raikou- Since most people run the SubCM set, I'll use this as an example. Raikou can use Substitute to protect himself from burns, and then start a Calm Mind war with Suicune. If you even have half of a brain, you'll know who wins this one.
Zapdos- Even though Zapdos is the only one that can't protect itself from Suicune's burns in some way, Zapdos can still switch in, threaten Suicune out with a Thunderbolt, and Roost on the switch. Roost also guarantees that Zapdos can stay alive and switch in when Suicune is left.
Now obviously, no one in their right mind would send out Crocune with any of those 4 Pokemon on the opposing side. On the flip side, no half-competent player would leave in their Suicune counter in to die when they see a Suicune on the other side of the field. Roserade's, Shaymin's, and Zapdos' easy recovery options will make sure that they can be there for Suicune, and this is why I feel Suicune should stay down in B. It requires support, and it's not something like Spikes support, where you can set it up yourself. It's support that can only be accomplished if your opponent is stupid and doesn't know much about the metagame. This alone should warrant that Suicune should stay in B rank.