The Martian Admiral Sauvitare (sp?) from S4? specifically discusses how to hold the ring space and by extension all of the ring gates by holding the center of the ring with overlapping fields of fire from a single point.
He later defects from the MCRN after giving the Free Navy tons of Mars tech, makes a deal with the Free Navy, that they get the ring space but the MCRN defectors get the planetary system beyond one of the rings, but gets deleted going to Laconia (or wherever).
Basically the cost of capturing Medina station is essentially beyond the resources of the MCRN or the UN at this point.
I figure the series ends up with Marco either being killed before getting into Ring Space, or better still his whole fleet gets deleted trying to scramble into ring space, but the Solar system is basically at a standstill vs the Remnant of the Free Navy that holds the ring space as they cannot get passed those guns.
Drummer ends up being the defacto head of the OPA and Belter Nations.
Stuff is set-up to happen beyond the rings if the Laconia subplot indicates anything and sets up the conflict for the "final trilogy" of the series.