Once you reach a certain population number, there should be new corporations forming to take advantage of the huge market you created. I have 1m people in my nation right now and I'm the only corporation. I produce literally everything. I make factories even though I don't need to, because I need to increase employment. The AI is very bad at Survival Mode so it's just a matter of time for them to run into huge debts and the player can acquire them easily. Digital Age companies also don't play well in this DLC. Software corporations don't even do anything (except for starting R&D projects sometimes) until you start to sell raw materials so they can make DVDs and computers. I guess it makes sense that they don't attempt to mine, being software companies, still doesn't stop them from doing things that puts them into debt. Internet companies start new websites even though internet literally doesn't exist yet. Normal AI companies sometimes try to produce things with low necessity index (usually using large factories even though a small one would be a better idea) which only makes them lose money in a sparsely populated city.
AI is competent in populated cities though, so if new corporations started to form after certain population numbers, they would create a threat for the empire the player built. It could be a new game option. How many years must pass or what is the amount of population that must be reached for X amount of companies to be generated?
It's also unrealistic how there is only a few corporations active in a huge market. New corporations should try to take advantage of a young, quickly growing market instead of leaving all the money (and the trouble of finding people jobs) to me.
Of course, I could also suggest to completely rewrite the AI for Survival Mode but that sounds like too much dev work that should be spent for the DLCs IMHO.