Of course you can compare them! They're both phones with a notch! You can also separately compare their face detection capability. But that doesn't disallow you from saying one notch is smaller than the other.
I think he meant given that the features are not the same, it's hard to compare the physical aspects (and more technically, product specifications) "fairly".
I really don't think anyone was trying to disallow people from saying that one notch is smaller than the other.