Rank is just another way for the players to show the MC what kind of game they want. In AW, picking a playbook with a holding, following or other group attached to it shows that the players are interested in being linked to a central location or thing that stories spill out of, rather than actively engaged in seeking out adventure.
It seems that rank, with it's various advantages and drawbacks, is a powerful narrative tool that allows the players and the MC to set the political tone as well as the scale of the stories told. Muddy skirmishes between small bands of hungry men, or devious back room diplomacy and ranks of armored knights charging at each other across the fields of battle. Though power naturally accrues through rank, it doesn't grant any more or less personal agency. From the Outlaw Heir playbook, you could quite easily be a dispossessed nobleman or landowner who's family lands were stolen who now haunts the forests, robbing from the rich and giving to the poor, or you could be the scion of kings, a prince out to reclaim his thrown with the support of his uncle, a neighboring king with a huge standing army.
Two totally different levels of power, equally intriguing, right out of the box.