I actually like Rachel Zegler, saw her in West Side Story and she was great in it. When it comes to casting her as Snow White, I think she'll do great in terms of acting. Unfortunately, she was cast in this era of being "politically correct" and as reason her skills will be overlooked due to this controversial casting. Considering her appearance she won't be convincing as Snow White (as far I'm aware she's of Colombian and Polish decent, but it's evident that she looks more like Latina than Polish girl, which is fine). Most people will think that it's another casting to include POC - exactly the same thing as in case of the Little Mermaid regardless of the acting and singing skills of both girls which will be extremely unfair. I don't however like people coming for the looks of the actresses - we all have different standards.
Representation is important, but it's becoming annoying when you start putting POC everywhere regardless of the story or cultural and historical context in the name of "representation". I grew up in Central Europe reading Grimms' and Christensen's fairy tales and I honestly feel weird seeing those castings as I'm perfectly aware that none of the authors could have even seen someone from another race back then in Europe as there were almost no POC here. So I also don't understand why Walt Disney should make those characters as POC in his animations (regardless of him being racist which is a completely different story and I take your word that POC in the US were underrepresented). I could agree that in case of the Little Mermaid it could be a way of interpretation as the character is a mermaid (btw are you aware that mermaids were also described in the Greek mythology?), but it's difficult to stomach with regard to Snow White.
Could you imagine Tiana or Mulan being of white race? I don't think so. Personally, I think that it would be great if new stories could be created focusing on POC more as they would be refreshing and I'd also defintely watch them.
We have seen many examples when the POC were casted in historical productions (set in Europe) and I really don't mind and enjoy them, but when I see productions like that, I instantly know that they could be far from being historically correct (examples: "Bridgerton" - romance comedy; "The Great" - satire, or recent "Persuasions" tough this story was butchered and I don't know what it supposed to be). Also this argument of people not being the target audience isn't convincing at all - it's Disney - one of the largest production companies distributing its content on the whole world.