Sry Universo, but each building has the same profit. There is no reduction in profitability for building more buildings. I'll give an example.
You start with a Toy shop and build tricycles. It costs 2,155,000 to set up. With sufficient quality you'll net a profit of 110,000. So, on the first day you get a 5% return.
Later you have enough money to build a second toy shop and a second line of tricycles for 2,155,000. You'll profit the same 110,000 off the second set. Now you've invested 4,310,000 and earn 220,000 per wu. Still a 5% return.
Making twice as much money, you will build your third shop in 1/2 the time. Making an additional 110,000 per wu. By this time you've invested 6,465,000 and profit 330,000 --> 5% hourly return on investment.
But now you can build the fourth shop in 1/3 the time! ....
So you see how the rate of return is a constant 5% even as more money is invested into infrastructure. This is the definition of exponential. As your company grows so does the rate of investment and so does the income. It's totaly unstable and we would all make 6E16 if we could just keep up this growth rate for 10 days. Alas, they put the 100 square limit and so ends the early exponential growth.
The next phase of upgrading buildings is probably not exponential, but really I haven't studied it (nor will I) to see what kind of growth it is. If each level of upgrading took the same amount of time and money is surely would be exponential. But since each subsequent level takes more, it doesn't fit the exponential (or logarithmic) models easily. You would have to do further work to show what it fits.
And the last growth phase, the RL growth. Well, that doesn't fit any known function easily either. There are points where you make more money, no more money at all, less money, and insanely more money. In the low RL's it's hard to gross 5,000,000/wu. At RL 26 you can get twice that. At RL 39 you can get 25M-40M. By RL 45-50 some people gross 50M/wu. Just look at the newspaper for proof. You'll see Jikco, Stora Enso, and others pulling down huge sums of money every wu. Again, it hasn't been fit to any known function of growth.
In my previous post I called each of the three sections exponential, and each having a smaller exponent than the last. You noted perhaps correctly that the last two sections are not exponential. It remains to be proven that they follow any other type of recognized function though. Lacking any known function that fits, I've approximated them in my mind as exponential with a smaller exponent. Would it be better to say they are linear? Logarithmic? Maybe. Maybe not.
In any case I'd say the point is mute. I use the terms that fit best in my mind. If you wish to argue the point further in a meaningful way, you'll have to show some proof.
Best Wishes
