We are to clean Chris not tell them how crap it has been built. This surface may not have been cleaned for xxx amount years so with regular maintenance cleans it will get better. Pressure , dwell times , hypo percentage , temperture all do play an important part to achieve the goal.
I have no doubt that this will get cleaner with regular maintenance.
My own patio was worst than this . Now it is perfect with a little perseverance.
Accept , that on this job it has to fall within the budget for both parties . Ed