I am just pointing out something here, not good at spicing up flows.
Arceus Bug can OHKO Mewtwo and Darkrai at +0, most forms can't. Since Arceus Bug will go all out Offensive, he can even smash Defensive Mewtwo in one hit. Arceus Bug is a good check to Darkrai and Mewtwo. ( You mentioned Psychic and Dark but maybe mention both Mewtwo and Darkrai because they are common )
With the rise of Ferrothorn, Dark Arceus might not really take out stall teams by himself anymore, or at least with the use of Refresh. Dialga, Skarmory, Tyranitar, Excadrill and Terrakion are also rising in usage, hampering his sweeping process.
Mention how Dragon Arceus can hit even harder than either Dialga or Palkia after one Calm Mind on the special side. Good to say, Salamence and Rayquaza will hit harder than Dragon Arceus initially so you mention the bulk is that important, such as when tanking Lugia's Ice Beam.
Originally Posted by Fat arceus ground
Arceus has more overall bulk than Groudon, who is considered to be the epitome of walling in the Uber tier
Groudon is only the epitome of physical walling. Also the sun Groudon brings make it more useful as a supporter. Ground Arceus is more useful in Swords Dancing with much higher Speed and Special Defense.
Even though Arceus is known as one of the most threatening Pokemon in the tier, it can be a phenomenal wall: Wallceus.
You can mention even when they are so many walls in the Ubers tier, Arceus can easily differentiate himself from them. Arceus is faster than all of them and has a wider movepool. Only one who can use Perish Song.
No mention of Arceus-Steel being immune to Toxic Spikes and resistant to Stealth Rock? Arceus Steel can also set up on Blissey or Chansey easily even when they have Snatch.
Water Arceus is 2HKOed by Kyogre's Scarf Thunder and Specs Water Spout. You can damage it with a Thunder of your own or Grass Knot to beat Specs Kyogre but Thunder will knock you out. Scarf Kyogre is safely walled but Thunder might 2HKO you. If you bump into Calm Mind Kyogre with Thunder, Water Arceus has no chance of winning. RestTalk Kyogre will just set up on you.