Or like in case of Krennic's shuttle needed a new design for narrative reasons (it's simpler to cut the movie if the audience immediately knows who is inside that ship)?

Right! This is specifically why Darth Vader had his own version of the TIE Fighter.

Let me tell ya about scale, ffg doesn't give a single care about scale anymore.

(in an attempt to derail this topic from the get-go)

Source needed.

Star Wars Armada.

But to be fair they still don't have the two troop transports from Episode 7.