The concept of Delves is to be solo friendly. Why do Worldsoul memories require groups to be efficient? If I do one as a group, which is just a laggy aoe spamfest, I can easily reach the maximum reward of something over 200 keyshards.
I just did one solo with my more than geared warrior (611 ilvl) and got a little bit over half of that. Now the issue is not that im too weak or anything, the problem is that no mobs spawn. You sit there waiting 10 seconds for 2 mobs to respawn, so of course you cant get a higher score for the higher reward. Its just really badly done.
Spawn more mobs for solo players so you can actually get the highest score. Joining a 30 man group for a 5 minute lag AoE fest is not fun or engaging. They also rarely form as most people dont care about them much apparently. Its just an oversight that really needs to be fixed.
Also the worm in Worldsoul Memory: Reign of the Old Gods that sits at the edge of the waterfall cannot be killed by any melee spec because once you step in melee range you get phased out and he despawns everytime.