Can I ask you to elaborate on where you get this idea from please and what evidence you have to support it?

Refs dont get the dominant and surrender calls right 4 out of 5 times.
Rugby league in the UK is turning into the only sport where the attacker is trying to find the floor and a tackler is preventing this.. its backwards.

A second ref can police this so much better.

They do. By definition. And the fact that you disagree with them from the stands or your settee doesn't make it different.

I would imagine its the same as the officials in the round ball game.
My friend is a lino at championship level and he has told me more than once that some refs will say 'I want offsides only'.
Maybe just maybe if they get told enough to 'just stand there looking pretty' then that is all they will do even when they haven't been told to do that.

They don't and just because you're a moderator doesn't make it different.
James Graham gets away with 20 times a game EXACTLY why the NRL brought the rule in after the Storm.

Sorry, but the only incorrect calls with regards this that I've seen recently have occurred in the NRL. We even recently had one ref shout dominant whilst the other ref shouted play on. I've also seen dominant called regularly when the initial contact has not driven the player with the ball backwards but not in SL. I can pull the NRL refs up on so many things that people claim they have cleared up by having 2 refs that it would take pages and pages to go through them all. Let me give you an example, 2 refs on the field, plus 2 TJ's and a VR and less than 2 minutes into the game last Friday the ref incorrectly gives a ball steal. Really working that isn't it. Oh and that offer of sorting out a course for you still stands!!!