Ok, to begin: I agree that the characters should downscale going by a few things. In this response, I will solely tackle the biggest point I have for the downscaling.
Winter and Pre-Maiden Penny.
Now, as a history lesson, we know that large enough gaps in power can one shot a character through their Aura, seen with Yang and Adam. We have also seen this with cases like the Atlesian Mech one shotting Jaune and Nora. It’s pretty well established that if the force coming at you is strong enough, your Aura will get shattered in a single hit or be completely ignored.
That said, let’s analyze the fight:
Cinder, with her Grimm Arm, casually stops Penny and throws her away. No scaling, other than showing that Cinder’s Grimm Arm DOES have a level of durability against blunt force, and that physically, Cinder is superior to both combatants here.
Winter steps up and they exchange blows. Cinder expresses her hatred of Atlas elites and gets a kick off that knocks Winter down for a while. She clearly isn’t going all out here, she’s posturing, living a fantasy of kicking down a person she hates. No scalimg, and again, displaying her superiority. In a 1v1, neither of these characters would do anything meaningful to her if she genuinely wanted them dead, other than holding out for an unknown amount of time.
Penny steps up, fails to do anything as Cimder just deflects everything.
Both Winter and Penny step up and here is where possible scaling begins. Cinder starts directly kicking them, similar to how she did Winter previously, but they are simply knocked back instead of one shot. Cinder at this point is grunting in frustration and anger because she wants to kill them and get on with her mission, her DREAM. Them not dying or having their aura flare/break instantly is showing a degree of scaling already, at least for their aura vs Cinder’s physical attacks.
Cinder then gets really mad, grabs them and breaks them through the wall. She drops Winter, throws Penny, and launches a flaming sword with the absolute intent of killing her either with the blade stabbing her through the skull or the explosion following it. When she performs this move against Penny, the entirety of her focus is on killing her. That flaming sword exploding is doing so with the force of her maiden powers, aura and semblance behind it. Penny is blown away, but her aura does not flash up, signifying the hit is painful but not enough to debilitate her.
Penny comes back up and Cinder is breathing angrily, a sign that she is exerting herself. She is not being casual and has not been casual for this fight, at least since the time she grabbed their faces to now. She is PISSED that Penny is alive. She wants Penny and Winter dead. She has been trying to KILL THEM.
Right here, at the moment Cinder rages that they are not dead, is where my belief they should downscale comes in. Them not dying or having their aura break = they are comparable enough to Cinder at her full power that she is pissed they don’t die sooner. Otherwise, imo, she should have her intelligence reduced to below average for not knowing how to use her own power.
Winter pulls up, her summon blasts Cinder back but doesn’t seem to do much but annoy her. More skirmishes, another fireball to her and she grunts in seeming pain before screaming angrily and rushing at them, one shotting the summon and destroying Winter’s aura with a fireball. Winter is tapped, cooked, weakened. She is weaker than Cinder and thus runs out of Aura first. Downed in not even 3 minutes of combat in a 1v2 where she was absent or knocked back half the time.
Plot happens, yada yada, pointless Maiden Penny, whatever, and Winter cuts off the Grimm arm. Note: the Grimm arm is a weak point despite its prior showing, and handling a punch =/= a sword cutting your arm off. Winter then fights Cinder and can deflect/block her hits, but without aura, is clearly getting completely outclassed and would absolutely die in about 15 seconds without Penny. Fight over.
So IMO: yeah nah, Penny and Winter should Downscale from Cinder. Aura is doing some heavy lifting, but in total, Winter took 4 hits while Penny took ~3, one of which was an absolutely bloodlusted exploding magic sword toss that Cinder wanted to kill her with. The fact their aura didn’t crumble immediately from her hits, and only after Winter had taken 3 attacks, spent aura amplifying herself and used it to summon twice (birds and sphinx? Thing?) shows that they can naturally take a few hits from her.
On the other hand, Cinder was damn near a walking tank to them. Their physical strikes are nothing to her Grimm arm, let alone her with Aura. She is pissed they aren’t dying faster, but she IS trying. Their attacks have little effect on her, showcasing her superiority, but hers aren’t having the effect she wants, which is their instantaneous death.