Correct! Sarah Palin didn't appeal to women.
False equivalence. While Palin was a woman, many feminists did not believe her to be an advocate for women's rights. This would be a little more comparable to Obama's strong performance in 2008 among black voters- underrepresented community gets excited about a candidate who either represents them in their specific issues or is portrayed by the media to be their advocate. As for Castro, primaries aren't general elections, and for Harris, I'm not even going to get into her issues with minorities.
And even if you believe identity politics makes a difference -- I think it can, on the margins, but it's not usually decisive -- I think it's perfectly valid to think of things through the frame of what will appeal to Mexican-American voters. They make up two-thirds of the Latino population in the US, and represent an even higher share of Latinos in the key states of Arizona and Texas. Someone being nominally Hispanic but not sharing a comparable experience to the vast majority of Latinos in the US might be a little helpful, but I fail to see how it would be more motivating than, say, Beto O'Rourke speaking Spanish and growing up in El Paso. The identification is no less tenuous.
Robert O'Rourke is not hispanic by ancestry or culture. Catherine Cortez-Masto is.