well ok but it must be a choice, not an imposition not at least for people who are willing to pay 1.500 usd
If you go through the the licence agreement of all other engines you can see yourself that they ask to display the logo only for the economic versions
What you mentioned is quite common in the industry, not only in games
The point is that the companies pay for such form of advertisement , they do not ask to be paid

As an alternative they trade off publicity and special low price
Last , I agree that GC badly need to be known in the market to occupy the place that this great engine deserves
The most powerful form of publicity are finished games
However as long as Indie developers display GC logo I dont really think that the few Pro users can be a serious issue