It is impractical for an experienced group of three to pull in a casual solo NB low on strategy going up against mobs in private dungeons. This has ruined several private dungeons I've tried and no wonder I don't get invited often when groups have already formed up. Restricting the PvE dungeons to 4 maximum period is a mistake. So I've tried private dungeons at least once if I can luck out and find a group but I've been quite unsuccessful with them, they aren't fun, and everyone in the groups races ahead of me leaving me feeling like I'm no real part of the group--which is true.
You're grouping with the wrong people RatsnevE. Not everyone dungeons like that.
Their goal was to group us up, if we're not grouping for whatever reasons, give people an option to group with an NPC.
The goal was never to group but the want to encourage player to group up the have say that never have as goal but the encourage player to group up to make it easy to complete thing.