I know you're not fully opposing it and all, but I can't help but be skeptical of the reasoning you employ that leaves you on the fence as opposed to being in favor of Gengar rising to A rank.
Saying a Pokemon is "super good" and proceeding to juxtapose that assertion by saying you're not quite sure if it's A level with the justification of name-dropping various Pokemon in A rank and labeling them "potent" is incredibly general and hardly proving any point at all, let alone convincing anyone on either side.
I think one of the key components of formulating an opinion when it comes to VR related matters requires looking at things in the context of the metagame and then looking at the other Pokemon in the tier in the context of the metagame. You appear to be doing this in an extremely condensed fashion, which I understand to an extent because who wants to post a fucking novel, but in doing so you neglected to provide any evidence as to why you think a certain way. If everyone where to post like this in the thread, then posting in the first place would essentially have no purpose whatsoever as you're bringing nothing novel or informative to the table. Moreover, expanding on what you mean by "super good" and why you believe all of the aforemention Pokemon are potent in the metagame while Gengar is not, comparatively speaking, would probably be ideal. Expanding off of this, I don't think I agree with your point.
I do think that Pokemon like Zygarde provide a unique offensive and defensive presence with various sets that can either be annoying or threatening to common team structures and Pokemon like Tangrowth and Ferrothorn are essentially defensive staples in the current metagame with incredibly useful defensive niches, utilities at their disposal, etc.. However, I think that Gengar is one of the best offensive threats in the tier due to the sheer lack of counterplay and while it does not receive nearly as much usage as any of the aforementioned Pokemon, it surely should be in discussion with them. There is nothing else in the tier that can spam its STAB quite as well as Gengar and given what it has at its disposal (speed, special attack, movepool, etc.), this makes it stand out as something that's able to do well against every archetype of team depending on the set and team it is used on. For example, Z-Ghost and the rare Black Sludge sets with Taunt, Wisp, Hex, and/or other utility moves can be incredibly problematic for slower, fat teams and stall, if used properly, while they don't have counters on offense, either. Additionally, Specs/LO variants are very threatening to balance and offensive teams as nothing really switches in and even specs can Trick Chansey or Toxapex on Stall, which adds onto the viability of these variants significantly. Finally, choice scarf Gengar is slowly falling out of favor and is not my personal Gengar of choice, but it tends to do well against offense as it can revenge kill many things and spam Shadow Ball while being the quickest thing in the battle most of the time, but it doesn't do much to bulkier teams unless it packs Trick or they're weakened significantly beforehand, admittedly. I'm well aware that many people shy away from using Gengar on their teams due to it providing minimal defensive presence, but it still can soft-check Pheromosa and switch into Tapu Fini once or twice, so it's not as hard to fit onto teams as one might think, in my opinion. Moreover, Gengar clearly fits into the context of the A rank and it is one of the most threatening Pokemon in the tier.
You're correct in that I didn't want to post a novel, as I do not care much for Gengar's position on the VR and didn't really want to do so. I do agree that the reasoning I provided was extremely general, you're right on that. I'll elaborate here since I realize that my reasoning was not convincing as to why I'm on the fence. I'm still not going to post a novel as I don't feel strongly on this, but I'll go into the more detail you requested.
The pokemon I named, Zygarde, Magearna, Ferrothorn, and Tangrowth, are all definitely potent in the metagame.
Zygarde is an extremely reliable win condition, Its great bulk combined with its typing also allow it to be a check to Volcarona and Zard Y. It also allows it to use defensive variants of Mega Venusaur as set up fodder, Celesteela, and non HP Ice Tangrowth as set up fodder too, among others. A team that is weak to Zygarde will eventually be swept by Zygarde. It doesn't even need any coverage moves, as Thousand Arrows is such an amazing move on its own, which essentially gives Zygarde 3 free moveslots, which can be filled by some combination of Substitute, Coil, Dragon Dance, Outrage, Extreme Speed, and Toxic. Zygarde's EV spread is also flexible, and it could go bulky or more offensive. It's an extremely versatile mon, and is very reliable at what it does.
Magearna is also very versatile. It can run AV, Z move, Specs, Trick Room, etc. It has an amazing Steel/Fairy typing that makes it only weak to Fire/Ground. It serves as one of the tier's best answers to Tapu Lele, and its typing and bulk allows it to check some other threats such as Greninja, Ferrothorn, Tangrowth, hell even Gengar. It also serves as a win condition with its Shift Gear set or Calm Mind set, or a win condition on Baton Pass teams as it's a very good receiver with Shuca Berry.
Ferrothorn has always been good, ever since its introduction. It's a fat, annoying mon, and without a way to reliably break through it it will just sit there and recover all its health and set up hazards on top of hazards. It serves as a check to Tapu Lele, non Hammer Arm Metagross, Lando-T, Tapu Koko, Tapu Fini, and many other mons in the meta.
Tangrowth has been on the rise in the past couple weeks, as its AV set checks like half the tier. It's one of the best pivots in the tier right now, and it's extremely splashable. If your team needs a Tapu Koko answer, just throw on Tangrowth! Ash Greninja weak? Throw on Tangrowth! What about Zygarde? Tangrowth! It's amazing ability in Regenerator and its good utility movepool allow it to check or counter all these things multiple times throughout the match.
Gengar, on the other hand, I've used a lot recently, and it has disappointed me to an extent. It's a solid A- mon, I can definitely see that, but it's almost dead weight against bulkier teams or stall teams if it lacks Trick. It can't really spam Sludge Wave when Mega Metagross, Celesteela, Magearna, Ferrothorn, Skarmory, Magnezone, and Mega Scizor all exist and are all very common. It provides minimal defensive presence, though admittedly it being a soft Pheromosa check is useful. Its lack of defensive capabilities make it harder for this thing to even come in, and its very weak to priority. I'm not a fan of the scarf set. When I look for a scarfer I'd prefer one that can handle Volcarona over anything else, and Gengar can't do that. Scarf Gengar is pretty weak power wise. The set I found most success with was its Specs set, and even then, I found its power level to be pretty underwhelming, and the fact that it's Choice locked was pretty annoying too. It has a good speed tier, but it only ties with Mega Metagross, leaving it to be inconsistent in that 1v1. Greninja can also come in on Shadow Ball once, and Gengar is forced out. When compared to the other mons in A, I find Gengar to be much less consistent, and dead weight in certain matchups.
