Anyone who believes in the coherency of the concept of 'cultural appropriation' is a cultural appropriation mythicist, since culture cannot be appropriated and, even were it able to be 'appropriated' in the way mythicists imagine, it would not be morally wrong to do so, but in fact usually morally neutral or morally desirable.
You say culture can't be appropriated, but then go on to say that cultural appropriation "the way mythicists imagine" is "usually morally neutral or morally desirable". You are claiming it can't happen while also claiming that it does happen.
'Cultural appropriation', as a concept, is incoherent and impossible.
In the first place,
culture cannot be owned so there is nobody and nothing to appropriate from.
Second, even if, in some sense, culture
could be owned (and leaving aside who has the right to make the judgment on who the owner is), copying, embellishing, reimagining, reinventing, and crafting anew from that culture is not 'appropriation'. It is a creation like any other and the moral owner is the person who created it.
Now, I know generally what the cultural appropriation mythicists mean by cultural appropriation. They refer to an activity where people, who do not share some deemed-to-be-important signifier of 'belonging' to a culture, copy or are inspired by elements of a culture. It is generally agreed by the mythicists that nobody in an 'oppressed' culture that borrows or reimagines something from the 'dominant' culture is appropriating it, but anyone who shares a signifier with the 'dominant' culture and borrows or reimagines something from the 'oppressed' culture is an appropriator.
It goes without saying that the mythicists find 'appropriation' 'problematic' and morally wrong.
The mythicists, of course, are morally abhorrent, but they're also incoherent. For example, Beyonce was criticised for 'appropriating' Indian culture in a video collaboration she did with Coldplay, but it is not clear how Beyonce is a member of a dominant culture that oppressed Indian culture, but perhaps Beyonce's Americanness is close to Britishness, and Britain did have an empire in India, and therefore she really is an appropriator.
So, culture cannot be appropriated in any meaningful sense, but yet I recognise the actions that cultural appropriation mythicists call 'cultural appropriation'. But even when I recognise what they are talking about, I do not agree with them that these actions are morally wrong. In fact, the actions are usually either morally neutral or morally desirable.