These guildies can be carried in raids, they aren’t complete catastrophes, but solo Delves just don’t work for them. They also don’t have time to grind crests so they just show up in whatever gear.
Lets say you only have 1 day you can raid and then the rest you can only play for 2 hours tops. They aren’t gonna be able to dent their gear and if a Delve takes them 30 minutes, they pretty much just spent half their game time in 1 Delve.