Gold and bitcoin are kinda complementary. Bitcoin strengths are golds weaknesses and golds strengths are bitcoins weakness. For example, gold is stable, whereas bitcoin is volatile, combining both is the best way forward for those who can afford it.
Bitcoin and gold are fundamentally different things. And bitcoin can never replace gold. Because the main idea of bitcoin is decentralization and the lack of physical value. So bitcoin can not be the basis of the world economy.
But sometimes the those people are claiming that the bitcoin and gold as the same commodity. It depends on the people already called the bitcoin itself. bitcoin was different in the physic but not for the value. it was having the same value as the gold itself.