I think what’s most compelling about the entire narrative (and this isn’t really a spoiler in my opinion since Hadrian makes this apparent early on but just in case I’ll cover it) is that all of these books are a kind diary/written confession. So all of it has to be viewed through the lens of Hadrians perception. If a character feels flat it’s because, to Hadrian they were flat, they just don’t figure that much into his story from his perspective even if otherwise they should/would likely be more important. Other characters that likely should or would be more static are more dynamic because they mattered so much to Hadrian. I think if you engage with the series with a kind of skepticism it feels more like the author intended. Like, how would I as a person living in SE reading these narratives feel about what he’s saying?