I generally agree with your comment about allowing marginalized character flaws, but I can't think of a significant trend where writers are criticized for creating flawed marginalized characters. If anything, the opposite is true-- marginalized characters are overwhelmingly criticized for being strong, smart, powerful or just being a part of the main cast. Look at the way fans treat any Femme/ POC characters who're part of the main cast in Star Wars or MCU.
Many "perfect" marginalized characters are in of themselves bad stereotypes-- the Model Minority Asians, or Magical Black people for example. The Mary Sue trope is in itself a double standard.
I do think that CIS/White writers are often afraid of giving flaws to marginalized characters because they're not sure where the line between flaws and tropes/stereotypes lies. I also think that marginalized people distrust White writers who are writing flaws with ties to tropes/stereotypes because there're already an overwhelming amount of misrepresentation of marginalized people by CIS/White writers which caused real-world harm to our communities. Often times, these writers do not have the lived experience, do not do enough research, or didn't hire a reader to help develop marginalized characters to be beyond the stereotypes. This feeling of distrust have always existed, just more amplified now; the feeling is usually justified imo.
I do agree that sometimes CIS/ White writers are unfairly criticized and that the level of online mobbing can go too far in comparison to a writer's mistake. However, much of these mobs operate on bad faith, many of them are themselves White (such as with the case of Lindsay Ellis) trying to stir the pot, virtue signal, or profit in someways.
And again, these criticisms are in relation to tropes/ stereotypes. I'm hard press to think of a criticism to just "character flaws."
I have received a few of these criticisms. To me the key is to know enough about what you're writing to avoid replicating stereotypes and tropes, provide the appropriate answers, let readers know your plans, and accept good faith criticism gracefully. Remember that Webtoon/Tapas allow for 2-ways communication: