I think there needs to be more distinction and instancing between the solo/duo "Delves" and the larger-group "Public Dungeons".
(For those of you unsure what I mean, take Glenumbra as an example: Bad Man's Hallows is a Public Dungeon, while Ilessan Tower, Silumm, Cryptwatch Fort, Ebon Crypt, Enduum and Mines of Khuras are Delves.)
The Delves, though public, are designed for smaller groups / solos, and so should have more instancing than they currently do to maintain this.
The Public Dungeons need a better system for organising the boss fights and their associated Group Challenge achievements to alleviate camping/farming.

Delves and Public Dungeons should use a different icon to indicate their differences. A support article on public dungeons says (paraphrased) solo dungeons will be marked as a single flaming torch icon and group dungeons will be marked as double flaming torches. This iconography was supposed to "indicate when an area requires more than just one player", but the Public Dungeons are mistakenly using the same single torch icon as the Delves.