Lando-I: from A+ to S: While I am not too certain in my opinion, I would support Lando-I rising up to S. Firstly, it has plenty of diversity, variety, and move options. Yes, it may not be able to run them all at once, but it can choose which archetype to break through with a quick trip to the teambuilder. It has a numerous amount of sets, from Rock Polish, Calm Mind, Stealth Rock, and just an All-Out Attacker - each can be tailored for the needs of the team. It can run HP Ice to murder Gliscor and Dragonite, Sludge Wave can hit a few select bulky fairies and generally will hit hard on neutral targets in general, Knock Off is a generally spammable move that Lando-I can use to bop the Latis and cripple Chansey - even if it's a bit more obvious of a coverage move that Lando-I may be running. Focus Blast, while shaky, has massive power behind Sheer Force, capable of OHKO'ing Air Balloon Offensive Heatran, and having up to a 50% chance to nail Skarmory after rocks. While I find that I use Psychic less for nailing things weak to it compared to a safety net move against possible switch-ins while finishing pokemon off, it definitely qualifies as extra coverage. Furthermore, it can 2HKO MSableye once mega evolved even if it uses Calm Mind in a 1v1 scenario. Okay, yes, its speed sort of holds it back, but it's a trollish one regardless and is enough to get the job done.
Raikou: from B+ to A-: Raikou has been steadily rising in viability over time, and I believe that it should do so further. If it recall correctly, then Raikou was first considered as a replacement for an offensive bird check - to be used as a poor man's Mega Manectric. Not anymore, as it's superioir bulk barring Intimidate and the ability to hold an item implies otherwise. It can also run a variety of sets to the need of its team. One of the more common ones is AV as a check to quite a few notable special special attackers such as Thundurus, Mega Manectric, Gengar, Starmie, etc. Specs boosts its above average power significantly and can gain momentum while dishing out powerful Volt Switches. Calm Mind is also another option, capable of snowballing through teams. It has a combination of being able to outspeed all the 110 megas, enough power, and versality. Yes, it has its flaws, but that's why we're not nominating it for S.
Starmie: from A- to A: As an advocator of Starmie throughout XY, my opinion hasn't changed. OU is quite short on Rapid Spinners, and one of its Offensive Spinners has to double as a Sand Rush sweeper. As far as I'm concerned, Starmie is the best offensive spinner in the tier, especially with its impressive speed tier. It can outspeed Latis, Gengar, Thundurus, and hit them all back hard. Analytic boosted attacks are practically a Sheer Force boost, and Natural Cure can be used on defensive and offensive sets to absorb status and reliably check Thundy. Not only does it have an offensive spinner set, it can also utilize a defensive set on less offensively oriented teams - although you should not overestimate its bulk. Furthermore, Rapid Spin has quite a few benefits over Defog. It does not activate Defiant, it does not remove your own hazards, it cannot be taunted, can finish off sash pokemon, which I believe is enough to make up for taking Life Orb recoil and making contact.
Hippowdon: from A- to A: Hippowdon is a very viable choice. Yes, he is somewhat passive, and yes, he has competition with Landorus-T. However, Hippowdon does not have a 4x weakness to ice, does not activate Defiant, less susceptible to crits, has a Stealth Rock resistance, phazing, and very importantly, reliable recovery. One of the biggest flaws that defensive Lando-T's have is that they are worn down easily from repeated hits. It has plenty of utility, from setting up hazards, spreading status, and repeatedly walling physical attackers. Some of these are very notable attackers, such as Mega Metagross. Just like Starmie, Hippowdon definitely deserves the rise.