A general note before I start: I've made the VR the cutoff for whether a mon should be included in this compendium because otherwise it's difficult to draw a line. However, there are quite a few changes that need to happen to restore that line, so to stop having to say that repeatedly I'm just saying it here.
Some outdated stuff:
Kartana is more prevalent than Bulu now. Tapu Bulu Checks should be renamed to Bulu/Kart Checks agreed
Aegislash, Ferrothorn, and Celesteela are no longer prevalent enough to warrant their own subcategories. Subcategories for steel checks are unnecessary. agreed
Strong Priority / Slow Attacker has fire turtle, but no fire camel :( Add Mega Camerupt to Strong Priority / Slow Attacker. that's an oversight yikes
Given Necrozma’s recent success, I believe it should be in the Solid category of Reset Trick Room, but this is not an important distinction so either is fine. The main reason I didn't move it was because the CM set has been more prevalent, but its value on semiroom teams is enough to move it up
Electroweb Tapu Koko saw decent usage this SPL, and I haven’t seen a Rotom-W in eighteen centuries. Swap Rotom-W and Tapu Koko in the Icy Wind/Electroweb subcategory. Agreed, also see the top note
Latias and Togekiss are iffy at best right now. Latias and Togekiss should be moved from the Solid to Shaky category of Tailwind. see the top note for Lati - as for Togekiss, it might be iffy as a mon but if you're using it, it's a solid provider of Tailwind. I don't want to define solid vs shaky as whether the mon is viable, but whether the mon performs the named role well
Mew has not been on a trick room team in ages. Mew should be moved to the Shaky category of Trick Room. agreed
Again, Togekiss is not very strong right now. Togekiss should be moved to the Shaky section of Redirection Support. see my previous note on Togekiss
Heatran has become less useful over time and has many commonly used resists. Heatran should be moved to the Shaky section of Trick Room Attackers. agreed, but not for the reasons you stated - Heatran is more widely useful now as a faster attacker with HP Ice or Flash Cannon and the Eruptran set is less commonly seen.
SD Kartana has been proven in SPL to be a big threat. Kartana should be moved to the Solid section of Setup Attackers. agreed
As grassy terrain allows it to eat an earthquake, get trick room up, and fire off weakness-policy boosted STAB attacks, Diancie should be added to the Solid section of Grassy Terrain Beneficiaries. I try to keep the "solid" section to seed users or *extremely* strong cases like Deo-A in Psychic Terrain, Nature Power Mega Camerupt, and Heatran, which has no chance at surviving Earthquake without it (or a Shuca Berry). Diancie does a great job in Grassy Terrain, so I'll add it to Shaky, but it's not a case where you should seriously consider adding Tapu Bulu just because Diancie is on your team.
I don’t have the replays to back this one up, but in my opinion Mew, Mega TTar, and Kommo-O are all Solid Stealth Rock setters. Agreed on Mew and Mega Tyranitar, but I think SR Kommo-o is a bit shaky - I'd much rather use Close Combat right now for Chansey/Incineroar or something like Flash Cannon that Human used.
Wide Guard may not deserve its own sub category any more. yep, this is outdated
As per several categories above, Rotom-W should be moved to the Shaky section of Ally Switch. see the top note
As a solid incin / TR setter nuke, especially when paired with Lele, Pheromosa should be added to All-Out Pummeling. see the top note - adding this now since it recently rose to the VR
Latias is not a good Z-Psychic user, Meloetta should be included with Bronzong for Z-Trick Room, and Cresselia makes a good dual-use of Z-Psychic and Z-Trick Room on the same set. see the top note for the first two, and I personally haven't seen Psychium Cress at all, so I'd like to wait until it sees some use before adding.