You are correct in the general idea is to help limit your options on what master to pick when it comes time for quick decisions. I realize that a master alone is very limited scope of the game, but it is near impossible to setup a method that accounts for your other crew choices. Sure you could say the crew box set, but there are some box sets that are terrible from a competitive standpoint. The other option would be to make a "core" crew, but some master can play dramatically different and will take very different types of crews (take Levi for example).
Additionally, the idea is also a guide on what you need to take within your crew to counter the master weaknesses.
Is the system perfect? No, not by a long shot, but the idea is to encourage discussion and ideas.