I really want to point out the fact that Raikou isn't even ranked. Raikou is, without a doubt in my mind, the most versatile weather Pokemon there is. What I mean by that is that Raikou can function well in Rain and Sun, while also functioning semi-well in Hail. While it does have to cope with a Rash nature, Aura Sphere is a very good move to rely on unlike Thundurus-T's Focus Blast. Raikou also has access to Weather Ball, which makes him an absolute monster under weather. A Base 100 Water attack boosted by the Rain? Ground Pokemon think twice about coming in. Combine that with an 100% accurate Thunder and Water pokemon don't want to switch in on the Weather Ball. Grass Pokemon? Taken care of by HP Ice for the most part. Sun? Why not have a very slightly less powerful Fire Blast that's 100% accurate? The combination of Fire, Electric, and HP Ice helps sun out tremendously. Grounds are hurt, waters are hurt, ices are hurt, and flying types are hurt. Most Grass and Fire types become powerhouses after those types are gone. If that's not enough, he has some other moves that have general handiness such as Volt Switch and Calm Mind. Let me take this directly from the OU analysis for Raikou:
"However, Raikou does have some notable assets that give it an edge over its competition. Unlike its competitors, Raikou has good 90 / 100 special bulk to compliment its offenses and give it the ability to take a few hits when needed. The extra speed is also useful for checking prominent threats like Garchomp and Keldeo, which Thundurus-T is unable to do without a Choice Scarf, and the extra power gives it an advantage over Jolteon. Aura Sphere and Weather Ball are two great coverage moves that Thundurus-T and Jolteon would love to have. Raikou even has unique access to Calm Mind, allowing it to boost its special power and bulk simultaneously, which in turn makes it a more powerful and more durable sweeper. Utilize these niches and Raikou will never disappoint."
Raikou has a strong niche in the Metagame as a multi-weather sweeper and bulkier and faster electric type. While I would like for him to be considered low to mid B Rank, he should definitely be C rank at least.