Okay, that's fair. However, I would argue that her being a legit 6'0 helps to offset that, especially considering that Vandersloot (5'8), Bird (5'9), and Whalen (5'8) were/are all a good bit shorter (which, in addition to their athletic deficiencies, hurt their chances of becoming better than average defenders). I would also say that Sabrina (5'11) is noticeably slower than Caitlin, which hurts her (Sabrina's) chances of being substantially better than average.
So if Caitlin is taller than the average guard and can move her feet better than at least one elite contemporary guard, then I'm not really seeing any reason why, from a defensive ability standpoint, she can't be held to a higher standard. No one's saying that she has to lock up Arike Ogunbowale for an entire game, but slowing her down for stretches/getting a game-changing defense stop on a player like that should be an expectation for a player who is to be heavily featured in MVP talks in the future. There are two sides to basketball.
And before anyone mentions it, Nikola Jokic (3x NBA MVP) is considered to be an average defender.