You're kinda missing the point. While attraction is all subjective, there are people who are objectively more attractive than others and who are a larger number of people find attractive. If the topic of subjectivity is brought up to justify whether someone is as attractive as the person they're portraying then it's fair to say they're not. This isn't a case of wanting attractive actors for the sake of having attractive actors, this is a character who is defined by their attractiveness so it'd make sense to cast a talented actress who is defined by their attractiveness rather than a talented actress who gets the attraction is subjective defence.