You have that so wrong, it is funny.
Funny, I was thinking the same thing about you.
All private groups, share one common thing you use to promote bonuses to Open - having to share.
I can, in ANY private group I play in, jump into a RES and there can be people there - so now I have to share, or move (just like in Open). Thus I earn less cash that play session for either messing about finding a RES without anyone in it, or having to share the spawns in one.
As for CZ, even in Mobius, I'm subject to PvP in there and also, the same share issue. I can jump into a CZ in Mobius and find 8 people on the other team, who'd you think is getting blown up first.... hint, not and NPC.
In my other private groups, same problem of having to share kills or depleted NPCs to shoot and waiting on respawns.
So, a lot of "Opens problems" affect private groups as well.
So it can be argued, Groups should also receive any bonuses added to Open - under the same reasons.
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Also in Groups, not just Open
Mobius has what, 8100+ members? That's the largest group and has, at most 2% of the total population in it. Assuming an even split, 33.3% in each solo, group, and open, which since we don't have any hard stats is the best guess I can make. Mobius has less than 1/15th the population of open, the chances of running the same amount of players is tiny compared to it. Even still, I'd support an increase to npc spawn rate based on the number of players in an instance.
You conveniently didn't talk about trading. in mobius traders enjoy the luxury of no pvp, whether legit pirates or killers. Since npcs are terrible at their job, even when compared to a below avg skilled player, there's no risk to those traders. So while bounty hunters and mercenaries, have to share, traders don't.
All you proved was npcs spawns need to be adjusted for group, as well as open. I never disagreed with you on that one.
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Two out of three modes share the 5% trade dividend vouchers. Who's to say that when NPC wing members are introduced (and hopefully the ability to wing up as a trader escort) that trade dividends would not extend to Solo as well?
Well you'd have to pay for escorts so there goes some or even all the bonus money, and most of the 5% bonus comes from trade vouchers. Wings of bounty hunters lose money since they split up the bounties.
Unless they implement hiring traders to tag along and carry cargo, the 5% bonus won't effect players in solo.