I meant I'm predicting that modeling monopolies/oligopolies as entities that try to optimize their profit is going to be unsuccessful.

I agree that fine-grained predictions of a firm or an industry's behavior will not be possible with such a model. But whether the model is good or not depends on what you're comparing it to and what you're using it for. So what would you like to compare it to? What is your preferred model?

To be more specific, lets take Microsoft. I think that for many purposes, it is useful to think of Microsoft as attempting to maximize long-term profits.