I don’t necessarily agree with that. I think the idea of draining life and healing it ties in well with the themes of selfishness and selflessness, which are central to the Saga. I think what is unique to the Dyad, though, is the ability of resurrection.
In the prequels, Anakin had a vision that Padmé would die. To him, that meant her dying was inevitable, and he needed a power beyond just healing.
And just because others have not used this ability in the films beforehand doesn’t mean it didn’t exist. Perhaps it was a technique lost and was rediscovered by Rey in the ancient texts. Or, the waning and waxing of the Force’s strength over generations has an effect on people’s ability to perform it.
And regardless if you cut the power out of IX, it won’t change the fact that Baby Yoda uses the power in the Mandalorian. And maybe he can do it because it is a child, and children have been shown to have an innate connection to the Force, just like the Dyad is shown to have in IX.
That’s all fair. I have a problem with the Dyad though - to me it feels like a cheap way to introduce two characters who are extra powerful, which I don’t think is fair game in Star Wars.
And while you’re right that we may just not have seen it during this time period, either we have an awful lot of media where it doesn’t happen onscreen (including where it’s particularly useful), or it’s lost and then remembered, albeit clumsily and relying on errata or assumption.
Definitely a good point on Baby Yoda though - I didn’t have a problem with that although it’s the same issue, I assume because of just how well the Mandalorian show managed to ultimately pull off a lot of similar things to TROS (including ample fanservice which didn’t phase me either). So there is some hypocrisy here. You could justify that as BY using a darkside power ignorantly, but the counterargument to that is that it relies on assumption, which I’ve already shot down.
I’m aware I’m not putting together a compelling argument here - there’s just so much of TROS which absolutely rankles me and combines to this ultimate feeling of it not just being bad but actively doing damage to SW. It’s an uncomfortable position to be in, having loved-tolerated so much of SW in spite of its imperfections for so long.