You just discovered the lack of overridden dependencies with Git submodules:
If Super depends on Core, its dependency of Core should “override” the ones A and B have with Core.
The only way to emulate that would be to create your Super project the way you did,
and to remove the sub-module Core of A and B.
(meaning Super depends now on A’ and B’, A’ being A without Core, B’ being B without Core)