Weber has infodumped about Sol's economic status a little bit more.
Here is the info dump.It would appear that Sol:
Sol system (in particular) attracts a lot of refugees and escapees from the less prosperous systems of the League and those under Frontier Security mandate. Once they arrive, they contribute to large pockets of undocumented, "under the radar" ghettoized poverty (a classic "underclass" which gets the sort of shrift underclasses traditionally get). The majority of Solarians frequently don't even realize that those pockets of poverty exist, and don't have any very clear notion of just how bad things are for the people living/trapped in them. They assume that there is a sufficient "safety net" to keep everyone afloat in relative comfort, if not precisely affluence, without realizing just how great a gap there is between what they think of as "relative comfort" and what the safety net in question actually supplies. Moreover, they don't realize how many of the system's poor are completely undocumented and, as such, largely ignored by the governmental support agencies. Nor do they realize that the Sol system has a policy of deporting non-citizens, which is one reason that so many of the people hiding in the various ghettos are undocumented in the first place.
We can deduce a couple things from this, if we make a basic assumptions like "People on the safety net know what is supplied."
1) The majority of people aren't on the safety net.
2) Just being in the
Solarian League doesn't mean you get to immigrate to
Sol freely. (Otherwise why would immigrants from other parts of the League contribute to the undocumented.) I think this points to both an independent Sol government, and one that takes a dim view of the rest of the League. (The later part which is probably good for future relations with Sol!)
However:
In addition to these relatively large pockets of extremely poor people, the gap between the income of the very wealthy and the average Solarian is stupendous. By the standards of the majority of the human race, even the poorest Solarian lives a wealthy lifestyle, but all things are relative. Klaus Hauptman, despite his enormous wealth (and make no mistake about it, his personal wealth is absolutely staggering on almost any conceivable scale), probably wouldn't even make it into the Solarian Fortune 500, if for no other reason that the people who do make it into the Solarian Fortune 500 tend to have been there for generation upon generation. For them, the mere thought of worrying about how much something -- anything -- costs would be ludicrous, and they live accordingly, for all intents and purposes completely insulated by power, wealth, and prestige from all of the unpleasant realities the rest of the human race faces. This is acceptable because despite the enormity of the gap, the average Solarian income and lifestyle is very comfortable and affluent.
So the safety net really isn't that bad, and then the majority of Solarians are a step above that!
Another factor in the lower Solarian per capita income (and wealth generation) is that the Sol system is much more prepared to accept inefficiencies than Manticore is. The Sol system is so huge, and so wealthy, and has so many people living in it, that it is essentially a "satisfied economy." I'm not saying that it's stagnant, or that there's no capital investment, by any means. What I am saying, however, is that the Sol system does not place the same premium on innovation that the Manticoran system does. There is a basic mindset that "we're doing just fine" and "if it ain't broke, don't fix it" which precludes the Sol system from being as "hungry" when it comes to innovation and basic research as Manticore, not least because the Sol system has such an enormous internal economy. Despite the fact that interstellar shipping in an impeller drive, hyper-drive equipped economy is incredibly cheap, it's still cheaper to produce goods locally, so even though the League enshrines the principle of "free trade," there are effective trade barriers simply because of distance and time in transit which tends to buttress (or at least subsidize) the inefficiencies hidden within the Sol system's economy. And the Solarian view (which is probably eminently sensible in a safe and secure society at the apex of the galactic political pyramid) is that the function of the economy ought to be to meet the needs and security -- and satisfaction -- of the people living in it. Solarian moral crusaders may be relatively rare, but so are Solarian ruthless robber barons, and the Sol system's labor force is more concerned with making sure that it has the sort of health care and financial security it wants, coupled with the least onerous working conditions possible, that it is with worrying about whether or not the Sol system is the leading economic powerhouse of the universe.
What all this means is that there is a vast potential for upgrading the Sol system's economy if changing economic or other factors should make that desirable, but at the moment, the Sol system is substantially less efficient at generating income (or funds for capital investment) even from the same sort of income sources (see my comments below) than the Star Kingdom of Manticore has traditionally been.
Also we know that the people of Sol place a premium on less work, over having more spending cash.
Presumably this will change very quickly if Manticore pops a fleet over the Alpha Wall in Sol and they don't either murder billions or lay down an Iron Fist. Not only that, it will probably make the industrialization of Grayson look minuscule by comparison. Vastly larger population, vastly better existing industrial and tech base, and vastly, vastly more spacers? Plus the lack of caked in misogyny/gender-roles holding back 3/4ths of the population.
Also, I seriously question the wisdom of trying to Iron Fist or genocide the people who presumably have everything learned in the Final War stashed away. "What this new strain of E. Coli turns into a insidious, incurable, deadly nanoweapon, when it infects someone from Manticore's military? Weird. The only symptoms anyone else has is improved digestion. Well, have fun dying horrifically. Let's just hope those Yawata Strikers don't attack while your military personal are dissolving into pools of delicious, nutritious yogurt. Seriously, this stuff is delicious."
tl;dr: Sol isn't like pre-revolution Haven. They aren't 70% dolists. A majority aren't living on the dole. Furthermore, a lot of the poor people aren't on the dole because they are undocumented immigrants from within the League. The people of Sol/Solarian League either place a higher premium on free time and nice working conditions than Manticore though.
Also the amount of wealth sloshing around in the Solarian League is utterly absurd.