So an Appeal to Authority and an exit. That's an effective counter.
Loki could also change into an old woman(not shamanistic), and if you're shapechanging waaaaaaay back when these myths were created, what other than humans and animals are you going to turn into? Turning into a salmon or a horse doesn't equate to shamanism.
I think some confusion could be avoided if we start with some core understandings:
1. The definition of shamanism does not focus on shapeshifting at all. Not only is it not a focus, it's not even part of the definition. That doesn't mean shapechanging
can't be part of a shamanistic culture, but that it's not core, or required, in that definition.
2. shamanism is just part of overall animism. They are not the same. Animism much broader (and why I believe, as do others, that shamanism is a term that shouldn't be used because it's more specific to only a certain few cultures, and teeters on cultural appropriation, where animism is more broad and still includes all of those aspects of shamanism).
3. The idea or concept of people changing shape is in nearly every culture in the world, many of those have nothing to do with how shamanism is defined. As mentioned above, Germanic and Norse mythology has examples of shapeshifting that have nothing to do with a spirit connection. The concept of lycanthropy is another example. Numerous examples in Greek mythology are another (Arachne for example). Celtic mythology is also full of examples of shapeshifting (not just the fairies, but many stories are around shapeshifting as a form of punishment). The list really does go on.
Those are all known objective facts. Therefore, and this part is my opinion and I admit it, I really don't think we should be using the term "shaman" anyway because the history of that term is pretty specific to certain cultures. Just like we shouldn't be using "spirit animal" because that is closely tied to North American indigenous cultures. I think the evidence also shows that just because something has shapechanging abilities or traits, it doesn't mean it's a "shamanistic" trait, and assuming as such is flawed.