They don't say that God has to be fair; they say that God is fair.
Since you disagree with how I read those passages, perhaps you can define what you mean by "fair".
No they say He is faithful , and indeed He is to His word and His promises.
What is Fair? Fair would not have been slaughtering people just because they were on land that he wanted to give to Israel.
Fair is not playing favorites like he did when he gave the birthright to Jacob..
Fair is not giving one nation a way to atone for sin and leaving the others in their polytheistic religion that are an abomination to Him.
Fair is giving the higher wage to a man that worked all day in the field and not treating them all the same
Fair is having mercy on all people , not just who He wants to have mercy on.