First off, I'm not touching the voting on this thread with a thirty foot pole, it turned out not-great ("no u" fight) last time.
That said. I will offer expertise for the D&D verse.
1. Beholder scales to a baseline of 8-B due to Sunburst. It was calc'd by WeeklyBattles some time ago. That said, newer feats will cause the Beholder's tier to shift to "At least 8-B, likely Low 7-B" due to scaling to dragons' feats that were calc'd (assuming they are accepted). Fight results for the 8-B tier would still be added, since the dragon feats were called into question over timeframe (basically, it isn't stated what the timeframe is, and some of them take longer than others, so Low 7-B is merely a "likely" and not a definite. 8-B stays as we can say for sure it is at least 8-B)
2. We discussed this last time. Anti-magic cone negates both magical and supernatural effects, including those not based on magic (i.e., psionics and the like). Based on this, there's no reason to assume it would not work on something supernatural in another verse. Even our experts are solid on this, and the ones who were hammering this point in weren't even voting to stay objective (Azzy and Qawsed). Psionics vary depending on the edition you bring up. D&D just likes ******* with our systems, basically.
To be clear, no, it does not affect an undead's inherent abilities purely because that is something they naturally have as magical beings. It doesn't negate magic that IS the creature, so to speak. However, a lich attempting to use magical spells (or even mind powers or whatever the hell you wish) would be unable to use them, as they are not inherent to that being.
3. Cherry picking isn't really a thing here, sadly. Abilities do indeed change depending on edition to edition, but D&D has thus far been treated as a most consistent basis. 5e being the latest edition... that's not the most consistent thing. Otherwise, you'd be correct. If you find more sources, I will look through them.
4. Looking at your "psychic" source... you're wrong. That is a Mystic, not a Psionicist (which is a thing).
For example, this is the SRD (System Reference Document, meaning basically open source WotC content for D&D) for one of the other psychic-type classes. It never once references magic. So... yes, the Mystic is a magical class, but not ALL psionic classes are magic.
Here's a better attempt to explain SRD. Basically, the company releases it so individual users can make use or manipulate it for their own games. WotC does it a lot. So, yes, technically the Mystic would be affected, the Psion would be equally affected, despite not being magical in nature (and being a pretty garbage class, IIRC).
5. Other knowledgeable members for D&D would include Aeyu (staff), Qawsedf (super-source-finder), Azzy (you know who it is), Xulrev (new user, pretty good with D&D) and ZacharyGrossman (dunno much about him, but he's been active on the revision threads so he might be a good person to ask).
I'd like to not be asked into the D&D vs JoJo fights, if only because JoJo is so... we'll call it heavily beloved by people of this wiki. Debating is not worth hurting others' belief in what they love. Cheers folks. If you need anything, feel free to ask~
As a very brief side note, I apologize for the late delay (was out all day) and won't be here tomorrow because, oddly enough, D&D session.