Reskimmed BatS bc I needed to do panel gathering for an ask and I'm still struck by the fact that they could have easily had duke say "my mentor, my dad" or smthn to that effect when Batman came in for that final save. But they chose "my mentor, my friend"
Because for a comic so defined by relationships, the ones he has with his family, with Izzy vs Riko, the uneasy start to his partnership with det. aisi; they could've easily shoehorned a 'chosen' father-son relationship btwn bruce & duke to contrast against the Gnomon reveal. If anything that would be exactly the expectation, that kind of story beat is a trope for a reason.
But Duke's chosen father is Doug. And that does make a difference. His relationship with Bruce is not lesser for being a mentor & protege rather than father & son, it's just different. And god if the greater majority of this fandom was really as obsessed with the Found Family trope as they claim to be, they'd acknowledge that this difference doesn't matter on whether you "count" duke as part of the batfam. Recreating the nuclear family is NOT the end goal of a Found Family trope, and it never should be.