Worldsoul Memories and Special Assignment world quests shouldn’t require groups. The content that leads up to them (delves and world quests) are all soloable then you get to the end, where the real reward is, and you need to find a group to assist in killing the Elites.
Worldsoul Memories you get pulled into another phase where you’ve no idea if other players will be around or not, with multiple Elites spawning to increase the rewards.
One of the Special Assignments requires killing Elites to farm fuel, of which you need 15(!), only to get ported to a new area to kill an even stronger Elite.
Solo content shouldn’t lead to rewards that can only be obtained with a group, or solo’d slowly as a tank. Maybe this will change with stronger gear, but the principle still remains an issue.