So if that is the case, what is to stop miners from just using their own versions of Bitcoin software running rules that they want? If they collude with exchanges and all just work together to make a digital gold version of Bitcoin that does exactly what the biggest economic players want, isn't that the death of Bitcoin?

Legacy chain. Core explicitly wants to add more and more "functionality" to BTC, hence the derogatory name "Bithereum".

Is Flesh Simulator on here yet?