Its called risk vs reward. I'll do this step-by-step.
Risk versus Reward isn't actually nearly that important, specially in games. Well made games will, instead, give higher rewards for doing things that are (supposedly) more enjoyable, as a way to guide players towards it and incentive them to give it a try. Risk or difficulty for it's own sake usually isn't rewarded, or at least not with anything worth more than just bragging rights; in fact, some games intentionally reduce the rewards for taking on content that is above the character's level in order to drive players towards more appropriate content.
And here is the snag: is Open more enjoyable? For some it is, but for many the chance of PvP ruins it either part of the time or all the time. Which makes it a very bad choice to offer increased rewards for Open, it would only serve to attract to it players that don't enjoy it, making them burn out with the game faster.
Besides, giving more or better rewards for tackling harder content is counterproductive in itself. It means the players that go for harder content will often get an easier game instead, because they get rewards that make the game as a whole easier, turning the difficulty curve on its head.
Lets start with risk. Do you agree that open is more risky?
Yes, it is, by definition. The fact that you can be interdicted / hunted by other commanders... that's a risk that you are willing to take when playing in open. Solo is safer. Really, there's not even an argument to be had here.
Actually, due to both the added firepower in a group and how instancing and matchmaking works, Open in a wing is less risky than Solo in about every situation. And, for most of the galaxy, even playing alone in Open is only marginally more risky than doing the same in Solo.
Thus, if you think the rewards in Solo should be reduced due to the lower risk, then the rewards for players in a wing in Open should be reduced even more.
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For me at least, current game without proper client-server architecture would be good enough, as long as it is always on-line. There are issues with P2P, but the main issue is the way the game plays in this combined universe.
I view the whole issue as a relic of no "offline" game fiasco, and in the end we do not get either offline nor a proper on-line mode. At the beginning of the whole thing, I thought that I needed time to decide whether this half-baked mode can work, and it did work during the exploration of game mechanics phase, but now that this is done, for me it kills ED.
It may be in the end, that not providing offline mode, and the way it forced their hand, ends up very costly to FD from an angle they did not expect. Officially they still do not recognize/admit it as an issue.
You really need to get your facts straight. The intent has always been to allow players to select who they play with and change their selection at will, including the option to play in solo, and allow all players to influence the galaxy regardless of who they choose to play with; the promise of an offline mode came later.
So, the modes and mode changing, together with all players influencing the same shared galaxy, were the core of the game's multiplayer proposal from the start.