Won't comment on the right balance, but I agree with Uncle Joe, corporations shouldn't be too profitable.
With Solver's fix, in big cities (25+) the maintenance of a corporation consuming around 20 resources is about 60 gold => 30gold after courthouse. You'll get around 40 commerce worth of bonuses from 20 resources. That nets you 20-30 gold/beakers for a domestic corp branch if the HQ is in Wall Street city. That's quite a lot. And its 50-60 gold for a branch placed in a foreign city.
Before the fix, the figures would've been around -15 gold for domestic branch and +15 gold for foreign branch, with 1900 inflation (around 140%). This doesn't sound bad to me really, but when the inflation rises, it goes out of whack.
I hope the designers keep couple of facts in mind when rethinking corporations:
- Don't make them like religions (spammable)
- The AI most likely doesn't know how to use them efficiently, don't make them too powerful weapon to cripple your opponents economy or boost your own
- Free market needs to be competitive with state property, so corporations must be of some use
Just my hasty 2c, feel free to correct my calculations based on a quick analysis of a late-game save