What you're missing is that if you are evaluating the non-trivial investment, you can't disengage it from what makes it a non-trivial investment if you want to do a an honest (thorough) evaluation.
The investment is relevant only insofar as it renders an assault on a PoW-coin unprofitable, for the defense from an attack is what keeps the coin from being valued less for its having suffered some manner of compromise therefor.