I personally (repeat, personally) don't consider the casting of MCU Scarlet Witch and Quicksilver as whitewashing because I don't think they were ethnicity-specific characters, not with their multiple parents and origin stories (especially prior to the Axis retcon, which caused the Maximoffs to be more important in their backstories than before because of the MCU versions). But if the MCU tried to graft those elements on to their version of the characters, then it would become whitewashing, or something like it.
It would be like if the MCU decided to give their version of the Ancient One (which clearly does count as casting a white person in a part that was originally Asian) some Asian elements in their backstory to make up for the casting. It wouldn't please anyone, those who liked the casting or those who didn't.
It will be interesting to see how this plays out in the casting of MCU Doctor Doom, though, since that part of his background really has been there almost since the beginning, but would take incredibly careful handling to avoid all the crude stereotyping.