Talim was included because she was left out of SoulCalibur V, and the same goes for Zasalamel. As in, completely left out, without any even possible substitute proxy, like Patroklos could be for Cassandra, and Leixia/Xiba/Natsu/Alpha Patroklos/Pyrrha were for Xianghua/Kilik/Taki/Setsuka/Sophitia. Beyond that, though, their inclusion does not change anything in the timeline, nor are they doing anything that takes place during or after SoulCalibur II.
Your last point disregards that while yes, SoulCalibur II-IV all take place within the same year, the story approaches, but does not start SoulCalibur II. What this means is that the age argument is null and void (except SoulCalibur V people, of course), but the events argument is still quite valid. Anything that directly involves or is contingent upon events from SoulCalibur II-IV can't be included in SoulCalibur VI's Soul Chronicle, because it wouldn't have proper context. It's very likely that SoulCalibur VII will cover 1590-1591, and maybe some years following 1591 to show aftermath of those three stories, but that is a looooooooooooooooong year, and it could feasibly be just that year, and still have plenty of content.