The degree and amount of design doesn't necessarily reflect the degree and amount of importance to play at the table.
What the degree and amount of design reflects is simply the amount of abstraction required. Combat has to be completely abstracted, as does magic (hence the many pages devoted to magic and spells) as neither can be done in reality and most of us have very-limited-to-no real-world experience with either one. Exploration only needs a certain amount of abstraction as we mostly already know how it works via experience in reality. Social needs very little abstraction as not only do we know how it works but it can be played out in person at the table. Downtime - the fourth and all-too-often-ignored pillar - is a mixed bag; it's the pillar that usually gets far less design attention than it deserves.
After that, it simply comes down to the amount of granularity the designers want to put into their rules and guidelines for combat, magic, and to a lesser degree exploration and downtime.
In terms of play focus, each pillar can be emphasized or not at any table based on how they want to play.