I strongly agree. Riot had been doing a good job lately of avoiding "blank-slate" retcons, but that's certainly what this looks like. The Poppy established by prior lore is a character defined by her gruff determination. This Poppy is defined by her anxiety and lack of confidence.
The most charitable reading I can manage is that this Poppy is sort of a "prequel Poppy", depicting her as she was earlier in her journey. (Though that journey itself is now also disrupted; it's not clear how you'd fit this new lore in with her prior origin story.) But how long is it going to take Riot to "catch up" with the old lore? Almost certainly years, rather than months. Unless and until that happens, Poppy is effectively Trundled.
It's not really even about new Poppy being better or worse than the established Poppy. It's about her being drastically different. This new lore is not functionally backwards-compatible, so to speak, and therefore invalidates years of community creativity and investment. Every story, every piece of artwork anyone created that relies on Poppy being the dour, diehard Iron Ambassador is now invalidated. Everyone who became invested in Poppy as a character now has to see her erased and replaced with a new character with the same name. That's not a nice thing to do to a community. It shows a certain measure of contempt toward, or at least indifference to, the community and its history.
This new character may be a really awesome character. But why not make her fully a new character? Make a new Champion with this "bearer" schtick. Let Poppy be Poppy.
EDIT: I feel stupid about this, but…uh. I wrote the above based on what other people had said about the VO, as for various reasons I couldn't actually listen to it myself. Now that I've listened to it, I have to say, it does sound like Poppy to me—just a younger Poppy. I don't have too much trouble reconciling the two Poppies: this is Poppy in her younger days, while the prior lore Poppy is what she becomes after she's replaced some of that gung-ho enthusiasm with steady resolve.