2-The Roaring Knight; portrayed as so far above the Fun Gang that fighting it is literally pointless because you can not win, no matter what. One-shots any CH3 Fun Gang members under normal circumstances, such to the extent that you need a full-revive item to revive Susie and Ralsei, if one-shotting them wasn't enough, reducing their HP to -999 is just crazy, and with normal, casual attacks at that.
I'm not sure the "casual one shot" is entirely true. It's definitely possible to survive most attacks when DEFENDing, especially with good equipment, Shadow Mantle or not, & Susie, with good Equipment, can throw out a Rude Buster (Thus not having been DEFENDing.) & survive a hit from around full HP or slightly less, even from stuff like Tracking Swords or the fierce winds.
The -999 is also a bit suspect as evidence of stats, especially if it's possible to not get one-shot when UP; We see it get called SWOON when it occurs, as opposed to DOWN when a normal DOWNing happens; The different name suggests a different effect, & this is backed up by SWOON disabling passive healing/Regeneration that normally occurs while DOWN.
I definitely do think The Knight is superior. At the start, The Delta Warriors have their damage dealt reduced to 20%, & they regain 1% per turn (0.5% per turn on Rude Buster, IIRC.), for up to 15 turns, up to a maximum of 35%. So maybe they're just unnerved?
But ultimately, they only do 20% of its HP, Susie is in disbelief that they won before she gets arrogant, & evidently, even a casual Knight is holding back, considering that after it sees even its spectacular Hyper-Goner-esque charged up final move fail, it just takes them out in a cutscene, maybe while they're off-guard, maybe it's just hitting really hard.
& of course, there's the case that it was holding back less, or even not at all with the cutscene attack, because The Knight wouldn't have to worry about hitting Kris or the SOUL too hard that way.
It's also possible the one-shot threshold in Deltarune is very high.
The Knight even thought that Susie's threats in CH4 were laughable, showing just how much of a gap there still is. T(hough if Gerson was fighting with the Fun Gang I think we'd win)
Susie's threats were that it can't beat them in the Light World & they just have to get past it. Considering The Knight abducted Undyne through the Light World, is physically much more unlike a Lightner than Kris, Susie, Noelle & Berdly, suggesting it may be unlike Lightners & whatnot that they understand, & it had the option of just making a Titan there to impede them, I think it's reasonable to believe it was laughing because of those reasons.
Not to mention, it spends all of Chapter 4 attacking from a distance, while they're helpless climbing, or literally in the dark. Though I can believe this is just pragmatism, even if it isn't some sort of bizarre goading tactic or something. I don't believe The Delta Warriors are at all close to The Knight's equals, but if there's any risk, why take the chance?
5-Tenna; most likely superior to any Fun Gang member individually, however of course it's worth noting that the Fun Gang members are stronger in CH4, so we don't know how he would far against them by then. But I personally doubt they'd become strong enough that any of them could individually beat him.
It may be worth noting that Kris seems to normally be holding back against Tenna; They do about triple damage to him with ATTACKs after completing the Sword Route. A possible reason for this is The Sword Route is where Tenna blabs about a deal, collaborating with Kris & The Knight, & in doing so, informs the SOUL; Kris could be doing extra damage via Rage Power.
But I can believe Tenna being superior to each Delta Warrior individually, even if Kris is holding back.
6-Spamton NEO; effectively the same as Tenna though I'm a tiny bit more skeptical that the Fun Gang members haven't surpassed him...well, maybe not Ralsei but Kris and Susie. Especially Kris considering that Kris did hold their own against Spamton NEO on the Weird Route and has grown significantly stronger since then. So I'd say Spamton can be as low as 8.
FWIW, Weird Route Spamton NEO probably is one where Kris did get serious, just because they don't use X-Slash anywhere else & Spamton was not only obstructing the Fountain but after the SOUL, which Kris may seem bitter towards at times, but ironically enough, I'd say, also seems possessive of. Some think there's a correlation between X-Slash & the post-Knight SWOON slash, due to the SFX seemingly being speed-altered versions of the same sound, but I don't think that the SFX stuff is evidence we can officially use yet, even if there might be a case based on X-Slash.
But yes, Kris definitely couldn't get past the Blue Light Specil alone, & Spamton Neo being a superboss otherwise.
She also straight up bench presses a CAR casually in the Light World which...doesn't need elaborating. I think she'd be 5 on this list in actuality.
IIRC, it's a stack of cars.
Sorry for any bother with this long response of mine. Besides what I said, I don't think I have other issues to bring up about your rankings.