The word rab translated as lord is more closer to father then lord. Tarbiya for example refers to the raising of children.So According to Islamic beliefs;
1. Jesus Christ prayed bowing
2. He preached the "One God message" monotheism
amongst others but forgetting the fact that he also referred to God Creator of the universe as his father which goes against the principles of the Islamic faith.
I know some would say its figurative sense but the hundred-million-dollar question is this;
Is Allah a father to anyone in any sense?
Qur'an 5 (Surah Al-Ma'idah) verse 18
Rahman is linked with the word raham which means kinship and refers particularly as well to a mothers womb.
So you have the word rab which mimics how the word father would in terms of raising kids.
And you have the word rahman which mimics how much compassion a mother feels for her child for all creation.
The word father in that time and place was being taken too literal or in a sense which god favors certain group over other.
The sense Jesus meant it could be a combination of rahman and rab.