Ah, you mean the possession. You can't do that unless you possess more than one Month. Currently, Yuri doesn't have the real Black March, only the Green April. She can't do that.
Besides, it's not clear if the reason Hell Joe considered that version of Yuri more of a threat was because of her raw power, or because of her ability to break the incomplete spells of Immortality. What I give you is that Months Possessed Yuri could be stronger.
You keep mentioning Top 500 Division Commander Cheonhee, even though none of the Division Commanders have had their ranks revealed. Funnily enough, the only confirmed Top 500 (at least before retrieving Green April) is Yuri, the one you keep putting far above that.
Yes, Elpathion is above Division Commanders. And yet, Evankhell implied that he + the rest of the Corp (which includes at least 4 Division Commander High Rankers + 4 Assistant Division Commander High Rankers + dozens, if not a hundred+ Rankers and powerful weaponry, alongside many Advanced Rankers) doesn't have a shot at beating a legitimate Top 300.
Elpathion also had his hands full at containing the mere residual shockwaves of Elliot and Evankhell's fight. That version of Evankhell was portrayed to be beneath Top 300.
No matter how you slice it, Elpathion is not remotely close to having the strength of a Low Top 300. I guess he could be within the Top 300 if by some chance he managed to kill outliers like Lefav, who aside from the super bullets, is not as strong as a High Ranker, but that's it. That'd just make him another outlier. Compared to legit people of this level, he's just weak.
- Floor Rulers: They're forces that tend to be comparable to Evankhell, as SIU said in one of his blogposts. Their power + influence should easily make them Top 300. That alone makes 133 Floor Rulers.
- Branch Heads, powerful warriors of the Family's Army, and other equivalent positions in the Great Families: Lefav implied that in order to surely be elected as a Branch Head in the LPB Family, you needed to be Top 200. The LPB Family alone has 20 Branch Heads, and from the looks of it, only 3 seem to be in the Top 10 warriors.
- Regents of the Great Families and Three Lords: Kirin, or the Ha Twins come to mind when it comes to Regents. Considering their hype, they're probably in the Top 50.
- Family Heads and Zahard: Duh.
- Matured FUG Slayers: Baylord Yama, Prime White, 1st Generation Slayers (including Luslec). Yama and White can stand up to Corps Commanders and the 1st Gen Slayers were said to be comparable to Yama by Khel. Their power + influence should be more than enough to register in the Top 300.
- FUG Elders: Khel Hellam is a Blue Hole, but Sophia wasn't noted to be one. If the rest of them are meant to be comparable to those two, some Elders that aren't Blue Holes can be within the Top 300.
- Corps Commanders: They can stand up to Jinsung and Matured Slayers, and command a Corp of the mightiest army in the Tower. They should be within the Top 300.
- Matured 13-Month Princesses, and perhaps other strong non-13-Month Princesses: Given their hype, I think it's safe to expect them to be in this league. Maschenny, Hagipherione, Adori and Enne are confirmed to be in the Top 100, at least via old blogposts. The rest have a pretty good chance to register somewhere at least within the Top 300.
- Top Warriors of Wolhaiksong: Urek and Baek Ryun aside, the organization probably has other individuals within the Top 300.
- Other Beasts that don't belong to any of these factions: Quadrado?
The Top 300 is already pretty crowded as it is. Some positions might overlap with others though, and I might even be forgetting some people here. The point is that a lot of individuals are there, but Vice Corps Commanders like Elpathion or McCage simply don't make the cut. We're talking about the cream of the crop.
Dokoko would destroy Elpathion. The guy is a Branch Head, aka a legit Top 200 (at worst Top 300).