In WH, when Roedran is gathering his army, Demandred says he is very busy. It also fits with his report ot Moridin in TGS, prologue, that he is gathering and will be ready (e.g. the Borderlanders are already gathered; I also don't see Demandred wanting to stay in Far Madding). Against Shara or Seanchan speaks especially that Demandred apparently didn't have the resources to rescue Semirhage. Besides that, we see Demandred wearing clothes of a noble in TGS, which might also point to Roedran's court. Murandy is strategical advantageous, at least if you want to attack Andor (Taim's cronies could help Demandred).

Besides that he likely controls Dragonsworn in the west, especially was behind Masema.

Oh, and Slayer killed Asmo. Probably on Graendal's orders. If Graendal had been the killer, BS had certainly revealed it in her last PoV.