Yes, that's a good point. I was assuming that without his wand he'd be making punch or claw attacks in place of it (which would probably put him slightly below Demogorgon), not just twiddling his thumbs, but I was thinking about the undead creation abilities and neglected to mention that part.
Yeah, the range issue is the major point. He can only grab it from 30' away, and then would have to keep wrestling with Orcus to try to get it close enough from him to take, and on rounds where he wins he can fly it 40' away from Demogorgon. Is that +1 bonus on the check for Demogorgon going to beat the extra 40' of movement when Orcus wins? I don't know. Swallowing it is a good idea when he gets it close enough. And then we he gets it that close, you'll still need to use the OOtA stats (again, assuming Orcus can punch) for a solid win.
5e is both vague and contradictory on deities. I have read all of the published material about them other than whatever may be in the adventures (though I am familiar with how Tiamat works).
In addition to the unclear and possibly contradictory statements about the divine status or rank of Asmodeus, here are some other contradictions off the top of my head:
-The DMG says Greater Gods are "beyond mortal comprehension" but this is in no way backed up by anything else. Specific greater deities are described interacting with (and even potentially being threatened by) lesser deities in exactly the same way as they were described in previous editions.
-The DMG refers to demi-gods in the literal sense as children of a mortal and god. It says they aren't really divine, can't answer prayers, etc. Then every other product talks about Demigods as a type of deity just a step down from lesser deities, who can do divine stuff, respond to prayers, etc--exactly like previous editions of the game.
-Volo's Guide to Monsters says that Grazz't the Demon Lord (who is not a deity in 5e) has more power than Demigods, and that becoming one would not increase his power.
I think the first thing one has to do to make any sense out of it is to entirely ignore what the DMG says in that sidebar on divine ranks. We have Greater, Lesser, and Demi-gods. We don't have Intermediate Deities. We have other powerful beings which aren't deities but are more powerful than demigods. Make out of that what you will.
I finally just decided to create my own philosophy of how to reconcile things (which involves ignoring some elements).