The idea is good, though the numbers are not OK. I would say, half the sectors + 1. That will give the strong guilds the chance to still dominate the map, which they obviously deserve, but will involve some more strategy, in order which sectors to hold and which to dismiss. And will partially limit the ability to do "the dance", which is ruining diamond league.
And of course, that must be paired with the ability to dismiss sectors.
Of course, nothing of this will happen and GbG will slowly become another useless feature, just like GvG, played only by a handful of people with no real life outside the game.