My guess is that the reason why they didn’t use the Sightless Eye to see the potential future is simply because they (both Lorath and Elias) lacked the ability to do so. Most likely only the most skilled priestess, someone who is incredibly skilled in the mystical arts, could utilize the Sightless Eye in such a way. That’s why Elias simply used the eye to see locations or communicate with people from afar, and why our character simply used it to spy Lilith’s position.
Also, it likely would’ve been better for Lorath to have not used to eye to find Lilith’s location, since we saw what happened to our character the second time we used the eye on Lilith and she temporarily trapped us. The only reason we managed to escape was due to Mephisto’s help. If Lorath had been trapped, I doubt he’d been able to escape. As such, it seems there’s great risks involved with using the Sightless Eye if one is untrained and/or incapable.
That is true. That said, we don’t know the origin of the soulstone used in D4 (whether it’s manmade like the Black Soulstone) or a remnant of the Worldstone (Inarius hinted that may be the case). It’s origin as well as whoever fashioned it, may play a huge role in how the stones operate. After all, the original three soulstones were created and fashioned by the Archangel Tyrael.
Judging by the dialogue and the campaign, it looks like the soulstone in D4 was created by Donan, who, despite his skill in the art, admitted to having uncertainty with it’s performance. Lastly, Astaroth’s soulstone was damaged (likely from our battle), and as such couldn’t be used to contain him any longer after his defeat, and as such may have been why he appeared in Hell in front of Lilith.
Tbh, Lorath hinted that we may see Duriel. He had speculated that we would have either seen Andariel or Duriel, at least due to the preparations and tragedy that Elias had carried out in Ghuulrahn, which was subjecting the entire city in untold pain and anguish, which serves as fuel for Duriel and Andariel respectively. Considering how Duriel and Andariel are twins (as far as demons go), it would’ve been odd to not see Duriel imo. That said, I did think it was kind of lackluster of our character to not have brought up their encounter of Duriel to Lorath.