Apparently its not that simple, because you have it all wrong.
When you are in a private group you are not in Open. You can't see anybody except the other people in your group. You will never share an instance with people that are in a private group you are not a part of. Solo mode is simply a Private Group of one.
I think you have it all wrong because what Im referring to all along is why enabling the switching of players to single player mode and open play at will is a gam flaw.
You come in saying that its all a core design and start posting quotes from the Dev about PRIVATE GROUP.
PRIVATE GROUP and " switching of players to single player mode and open play at will being a game flaw" are 2 different topics
We both agree that private grouping is an intended feature but what Im highlighting is a totally different matter