While I’ve been convinced of the Sentidrien theory for awhile now, I can see why Risk was more convincing than Ephemeral.
For starters, that scene in Ephemeral - while it did certainly look like Shadowmoth forcing Adrien to his will, he DID already have the akumatization mask. Only two people in the entire show have ever broken out of akumatization at that stage, have ever managed to defy Gabriel’s will, so while Adrien’s acquiescing in that scene definitely looked unusual, he WAS already having his will broken by the regular process of akumatization, and it wasn’t completely crazy for people to suggest that Adrien being under Gabriel’s control there was due to the akumatization, not the ring. Though there was never a really good explanation given for why ELSE the camera would make sure to focus in on Gabriel making that twisting motion where the ring would be (I never really bought the “he’s self-soothing” idea, especially with how this scene was framed).
Ephemeral did also have an earlier scene with Gabriel fiddling with the ring and ordering Adrien to make that speech and not leave, but again, while it looked very suspicious, it could also, maybe, possibly be him just being used to giving akumatization speeches and treating his son like one of his akuma victims as a result, and Adrien complying because well... his father is pressuring him, and Nathalie’s continued urging to continue with the ceremony.
Risk though? Risk not only had more clear-cut examples that couldn’t be as plausibly excused away as representing other things, but it kept on hammering its message incessantly.
1. Gabriel giving the ring to Nathalie, entrusting her with it and his son. If the ring was merely a sentimental object with no other power, it doesn’t make sense that he’d give it to her like this, and the wording implies that entrusting her with Adrien and entrusting her with the ring are connected.
2. Adrien being that upset, that ready to tell Gabriel off... and then getting that meek when Gabriel demands he changes. Normally Adrien would at least protest for a moment. Here, he doesn’t, it just seems like all the will and fight is snuffed out of him instantly.
3. Adrien telling Marinette that it feels like some “force” is stopping him from speaking out against his father, and he doesn’t even know why.
4. Felix telling Adrien that freedom is something he makes for himself, and that while Adrien can’t defy his father, HE can. Though this one is far weaker evidence than most of the rest (everyone knows that Gabriel determines what Adrien does, and he’d have trouble standing up to Gabriel even without the ring), it still follows along with the general idea of the Sentimonster Adrien theory.
5. Then the strongest evidence - that scene where Gabriel tries to order Adrien (well, Felix pretending to be Adrien) into submission, and falters when he realizes that he’s still glaring at him determinedly, with Gabriel’s face falling and looking almost scared, looking vulnerable when he realizes he isn’t giving in, and rubbing his hand where his ring used to be. And then Nathalie conspicuously pushing up her glasses, giving the audience a good look at the ring she’s wearing, and giving a similar order, which Felix obeys - still not totally sure whether Felix was faking that or genuine, but I’m betting on faking and he just knows that Adrien’s a sentimonster.
Big difference with this scene versus Ephemeral - there’s no other plausible way for Gabriel to think he can mind control Adrien here. He’s not in the process of akumatizing him. Plus, he outright FALTERS when he realizes that “Adrien” isn’t caving in like he expects, rubbing where the ring used to be, indicating that he draws some connection between “Adrien not obeying” and “him not having the ring”. But then when Nathalie DOES give him an order, he obeys, much like how he usually obeys Gabriel - and Nathalie isn’t surprised by this, that he gives in to her when he wasn’t with Gabriel. She seems to expect it.
6. Kagami’s whole rant about how Adrien needs to take control of his own life, not just follow orders, that he’s his father’s puppet and he needs to dare to cut his strings. It’s pretty on-the-nose.
A lot of these could be handwaved away individually, or at least not be seen as conclusive, but all of them TOGETHER in one episode? The sheer weight of it makes Adrien being anything but a sentimonster unlikely. Heck, at this point the only sliver of a possibility I could see would be that the rings have mind control powers inherently, not due to being an amok - but that seems unlikely at best. I do think that the rings absolutely, 100%, just from what we’ve seen in canon without taking into account outside sources, have to be able to force Adrien to magically submit.