But if I happen to be right, then covering the whole game under the MIT license will tremendously accelerate it being killed by clones/derivates that actually have a budget and man- and marketing power behind them.
TL;DR it's just a case of "better safe(r) than sorry"
Yes, it is true. MIT license does not have a clause which forbids that.
But, well, GPLv3 does not prevent that either. Someone with such resources could still do that, i.e. fork it and be more successful than TOL. The big thing which changes is that it is forbidden turn the fork into non-free software. The entity would be allowed to charge amount of money, but this would basically be meaningless for the community, because anyone could legally distribute a copy for free.
But I think with GPL this scenario is unlikely to happen. While “commercialism” and free software do not exclude each other directly, in practice they rarely come together (at least from my perception). Especially if copyleft is involved.
The GPL also has a danger which all copyleft-based licenses have. It is legally incompatible with a number of other copyleft licenses. It is (as far I know) not legally possible to combine stuff under different copyleft licenses, unless they are legally compatible. For instance, if someone wants to combine CC-BY-SA 4.0 stuff with GPLv3 stuff to create new stuff, that would be illegal (correct me if I am wrong). In these cases my guess is that you still have very good chances to negotiate a different license for your project, because the intentions are basically the same. But you may be out of luck if you can't find the copyright holder anymore. But I am not 100% sure about this copyleft thing.
In any case, I am not a lawyer, do your own research and make sure you read the license text first before you make a decision.