Corporations exist, if they have any purpose at all, to maximize profit. So this presents a sort of dilemma: their diminishing returns and fragile existence suggest that either they do intend to maximize profit but just aren't that great at it; or they don't have even that purpose which is evolutionarily fit and which they are intended to by law, culture, and by their owners, in which case how can we consider them powerful at all or remotely similar to potential AIs etc?

Ok, let's recognize some diversity between corporations. There are lots of different kinds.

Some corporations fail. Others are enormously successful, commanding power at a global scale, with thousands and thousands of employees.

It's the latter kind of organization that I'm considering as a candidate for organizational superintelligence. These seem pretty robust and good at what they do (making shareholders profit).

As HalMorris suggests, that there are diminishing returns to profit with number of employees doesn't make the organization unsuccessful in reaching its goals. It's just that they face diminishing returns on a certain kind of resource. An AI could face similar diminishing returns.

I bet organizations would work a lot better if they could only brainwash employees into valuing nothing but the good of the organization - and that's just one nugatory difference between AIs (uploads or de novo) and organizations.

I agree completely. I worry that in some cases this is going on. I've heard rumors of this sort of thing happening in the dormitories of Chinese factory workers, for example.

But more mundane ways of doing this involve giving employees bonuses based on company performance, or stock options. Or, for a different kind of organization, by providing citizens with a national identity. Organizations encourage loyalty in all kinds of ways.