Cool. I'm much the same way with the Spider-Men (Peter Parker and Miles Morales) books, though I think it works somewhat better in Steve Rogers's and Sam Wilson's cases since they've been friends and partners almost forever and, besides Bucky Barnes and Sharon Carter, there's no one else he'd trust more with the shield.
The spider is always on the hunt.
The thing with Marcus is he lacks the old spymaster thing that makes Fury's character. Marcus isn't a long-lived near immortal whose managed to have involvement in near every conflict since WWII and has been in contract with damn near every superhuman and agent.
But Marvel wants Sam Jackson Fury in 616 so they force it by just treating Nick and Marcus as completely interchangeable. Everyone treats Marcus as if he's the same guy whose been around since the 20th century.
Has Fury Jr ever been SHIELD director?
the easy fix could've been what they did with Miles just bring him over but tweak his origin as a WWII vet
also I think in my lifetime I have only read Nick Fury Sr. as the head of SHIELD for like one arc of New Avengers before he was replaced by Hill, so he's been MIA from a place of prominence for a long time