There is no doubt that the concept of a gadol/gaon/etc existed in various times, but to what degree it matters might have changed. I am wondering whether litvishe world got influenced by chasidim to some degree – having an identifiable leader seems to be popular.
In general, it is a republican idea: you ask a shaila of you rov, he asks of his rosh yeshiva, and he asks someone higher. This graph generates one or more figures at the top. Some may be specialized in certain areas, others – more general. Say, Rav and Shmuel were both gedolim, but we accept their psak based on the topic. Not sure whether the difference of expertise was apparent at their time or established over time. We see something similar now – there are people for whom Rav Chaim is a posek for learning, but for covid halokhos they don’t hold by him and go to ploni ben shapiro.