Ok I'd like to weigh in here since I have experience with support eleceus.
It doesn't deserve a main set IMO. What you could do is elaborate on its uses a bit more in oo, right now you're making it seem completely outclassed which isn't the case. For example, I run it on one of my better teams for a rather specific set of reasons. Firstly I use it as a Yveltal check as it switches into owing nicely (ofc I run a dark resist as well) and forces ygod out. It can switch into Ho-oh in a pinch as well (this one differentiates it from fairyceus), and remains a great Palkia check (and this one from Rockceus). The para immunity is a bonus. This is basically the entirety of what it does, so it's really too niche to deserve a main set IMO; what it does deserve is to be talked about a little more in oo. Since this analysis is already considered done, whether or not to do this is up to your own discretion. Just my 2 cents :]
Each support Arceus differ from the others by checking some mons anyway.
Checking Yveltal, Palkia, Zekrom while not being Ho-oh bait is a lot. Arceus-Rock and Arceus-Water are about the same.
Anyway, I'm wondering which move is the best between Ice Beam, Toxic and Will-o-Wisp :
- Ice Beam is the only one which allow it to break Gliscor.
- Toxic is great on him for opposing Arceus (most support sets, CM Arceus-Electric, CM Arceus-Ghost...) while Groudon and Lando-T won't like it too much
- Will-o-Wisp is nice against Groudon and Landorus-T