The title has no real practical significance. At least not since the days of Yehoshua (?). Similar to the idea of Gadol Hador it is a honorary term. If some whosays who is Rabbi X? You can respond by saying He is soooooo great he is the Posek/gadol/tzadik Hador.
Let’s take Rabbi Akiva for example. I think most would say he achieved a very high title. Does that mean that we always pasken like Rabbi Akiva? No. Psak has a certain system and does not care about titles.
When it comes to the title Posek Hador IMHO it is more about who has contributed the most to psak halacha. Thirty years ago R. Moshe had few rivals in the Ashkenazi psak ( R. Sholomo Zalman?) and R. Ovadia had no rivals in Sfardi psak. This does not mean that we pasken like them. It just means that their word carries a lot of weight and we consider them heavily when considering how to pasken Lemaaseh.