Verso and Gustave have way, way too much personality to be a blank slate self insert. It's not about who is the protagonist, but a self insert is literally (You) in the most literal sense.
For example, when the character is (You) a normal human being from earth with no powers or the character is an amnesiac human who can't remember shit. Even if you are a badass in the past, you are no longer a badass in the present. And if you lied and had evil traits in the past, then all of that was for a good reason and you no longer remember it, so the (You) of the present can be related to.
Furthermore, characters pander a lot more to the self insert. The self insert generally cannot do anything wrong. And, for example, about characters being for (You) for example if the character nearly drowned in the past, it's (You) who saved them and not the other character. This is EX pandering.
And japs do this shit with both the male and the female characters.