Very nice detail for Oda to not show Ace's eyes while leading Sabo's letter until he's shown to be bawling, especially since he's spent this whole flashback chastising Luffy for being a crybaby
After the flashback ends, Shanks will have a whole monologue telling Luffy it's okay for him to cry, which is the closest thing to Oda himself telling his audience it's okay to fully feel their big emotions. That's an important message for the target audience of young boys, and doesn't make the powerful, important characters of the series any less powerful or important.
