As per my previous posts - It's not just the RD. He represents the Stewards, all of the data analysts and other team members providing him the information. He himself is not making the judgements. Much like Borris and any other President of Country, isn't solely calling the shots.
They always have a trail of supporting evidence to backup the decision/s being made. [Not saying the decision is right or wrong]
But it's still absurd to suggest that rules can just be made up on a whim (especially ones that expressly advantage some drivers over others).
The trouble with Masi's decision is that there is no justification to it whatsoever, other than he wanted to manipulate the result outside the scope of the written rules.