I'm in agreement with a few of these nominations (stuff like Jirachi absolutely needs a bump), but I'd like to comment on some of the others.
Thundurus A- -> A / A+
Again, what made it worse? Colo doesn't like mixed variants, hazard control is easier in this meta than in ORAS OU, panic wave is still as good as ever, and the ground immunity is a good boon as stated before.
The simple response here is Cawmodore. Thundurus is an Electric-type that can't check Caw at all, as Cawmodore just sweeps right past it, meaning that it's often passed up in favor of Electric-types that sport Fire-type coverage or strong secondary STAB, such as Cyclohm, Mega Manectric, and Krilowatt.
+6 252 Atk Cawmodore Acrobatics (110 BP) vs. 0 HP / 4 Def Thundurus: 377-444 (126 - 148.4%) -- guaranteed OHKO
That being said, Thundurus is by no means a bad Pokemon, as Electric is still a fairly potent attacking type + it has the coverage to smack several of its switch-ins, but it fails to stop one of the metagame's most prominent setup sweepers (and can even find itself being used as setup bait if it doesn't run Focus Blast).
Suicune C+ -> B / B+
Again, what made this so much worse in CAP? Doesn't like colo knocking off lefties but otherwise beats, defensive cyc doesn't beat it after a CM or two.
The high prominence of Pokemon with immunities to Water really hampers Suicune in this metagame (Mollux / Plasmanta, the former of which is seen on almost 20% of teams and the latter of which gains a SpA boost and strikes back for massive damage). Nearly every Pokemon reliant on Water STAB is affected by this duo to some degree (Keldeo for example almost always runs Hidden Power Ground as its coverage option in CAP, whereas it doesn't really have a reason to do this in OU). Suicune could certainly run Hidden Power Ground itself to hit these mons, but this forces it to drop one of its other moveslots. Either way, I feel that Suicune's current ranking is fairly indicative of the type of support it requires in CAP.
On another note, non-CAP Pokemon in the CAP Viability Rankings aren't ranked with the sole philosophy "Look at a mon's OU ranking, see how it interacts with CAP mons, then adjust it up or down accordingly" and shouldn't be, because they're different metagames. OU is certainly the most closely-related metagame to CAP, seeing as it's our metagame minus 20 mons, but different playstyles still vary slightly or heavily in popularity in comparison to OU and we're often subject to completely different metagame trends. Sometimes similar trends occur, but CAP tends to lag behind OU a lot in this respect (an example being Tank Garchomp, which took quite a while to catch on in CAP when it had been a staple in OU for a pretty long period of time).
That being said, there are still a good amount of mons that deserve a shift that I haven't touched on here, so I'll likely post here again in a while or update this post.