That may not be entirely true, as presumably if you are part of a group you will be (slightly?) more likely to meet up with other players (and that's one of the big issues here, that some of these Open players never see anybody) in that group than if you are just in the Open group. I don't know, and hopefully others will jump in to correct me if that's not technically going to happen.
Hard to say, I feel sometimes like if mobius has 9700 genuinely active players it could well be much easier to meet people, though I would expect normal open to have more i'm just not sure it does
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Rckstr's primary driving motivation is, according to him, to meet more people. You don't even need a separate group for that. Jump into the Elite Groups forum and look for a group that feels suitable. Perhaps a group dedicated to the same Power or one that has a good history of inter-group encounters. One that plays in Open. Join up, meet up, enjoy.
Thats kinda my point, you can't make a group for that, most of the suggestions in the great debate here don't work as groups either. Hadn't thought about powers groups I guess I tend to just stay out of powerplay, even though I apparently support Hudson.