It's an ouroboros turning into a catch 22 you can't have an open system with high level of trust if the computation is trivial.
Ever increasing difficulty raises the bar so high that it centralizes a system due to the hardware requirements (there is no way to effectively mine BC today on standard computing hardware sorry) and their costs.
Look at the BC network now it's either huge centrally controlled mining pools or multi-million dollar mining farms which are controlled by individuals, this isn't decentralization of anything but computing assets as far the the pools are concerned.
Ever increasing difficulty raises the bar so high that it centralizes a system due to the hardware requirements (there is no way to effectively mine BC today on standard computing hardware sorry) and their costs.
Look at the BC network now it's either huge centrally controlled mining pools or multi-million dollar mining farms which are controlled by individuals, this isn't decentralization of anything but computing assets as far the the pools are concerned.