Exactly.
They're meant to be cutting out "clear and obvious" errors not re-refereeing the game.
It's ruining the game chalking off goals because someone has a toe nail or an armpit offside. Who actually thinks that's a good idea? Ditto going back through the action desperately trying to find the most minor of infringements as an excuse to rule out a goal.
Conversely however, when a penalty SHOULD be given by the on field referee but isn't, they rarely intervene for the reason that they claim it wasn't a clear and obvious error. It all seems to be geared up to chalk goals off whichever way round it is.