Latias down to A- or lower
Latias isn't very great in the current metagame. It loses to a majority of the pokemon in S and A rank (Diance, Clefable, Mega Meta, Mega Altaria, Ferrothorn, etc.) and what it does beat is often paired up with a Pursuit user such as Bisharp, Scizor, or Tyranitar. It suffers from a huge amount of 4MSS (wants to run Healing wish, roost, Psyshock, Surf, HP Fire, defog, Draco Meteor on the same set but can't) and its lack of power prevents it from being able to defend itself from pursuit users and bulky pokemon such as chansey, jirachi, and Klefki.
Tyranitar to A+
Tyranitar suffers from a numerous amount of issues in the OU metagame. Despite this, I still feel it should go back up to A+ rank, primarily due to its Scarf set. Choice Scarf Tyranitar is probably the best Pursuit user in the tier currently because of its high Speed, Bulk, and Power, allowing it to trap Pokemon such as Latios, Latias, and Gengar reliably, while also creating a 50/50 scenario with celebi. Its ability to pursuit trap these mons is invaluable support for two of the best mons in the tier: Landorus and Keldeo. It also has several other notable perks such as being somewhat versatile and providing sand support for drill, but its utility as a Pursuit trapper is by far its most notable quality.