I barely get any Seals from Bs really. Unless a bunch of A rank kills get bunched up causing a large break between spawn windows the stream of As is fairly consistent. I don't normally leave a zone for a B. I only kill it if I'm already in the zone. As a result I have more overall A kills than Bs lol. As for Alliances...read the notes properly. They are for the purposes of queueing to Labyrinth/ST only. It isn't explained as well as it should be but I imagine the "Alliance" outside of the instance just amounts to a flag that queues all three parties together for the raid and won't have any impact in the open world.