The concept of “One in Being” is incorrect. It is a statement of existence. There is no existence apart from God, so just about everything is “One in Being” with the Father. The Keyboard you are typing on, the grass on the lawn etc…
Substance is a statement on the Nature of something. That characteristic that set it apart from everything else.
While the grass on my lawn is “One in Being” with the Father, it is not of the same substance as the Father. It is not Divine.
Christ (as well as the Spirit) are Consubstantial with the Father, they share the same Divine Essence, the same Divine Nature.
So the old translation said nothing really about the Nature of Christ in relation to the Father, the new one does.
Why? It’s a nice concept, but it is not how the Church works.
When the Council of Nicea met, they created the Creed using the terms Homoousios\Consubstantalis. (the Council promulgated the Creed in both Latin and Greek.
This was back when both Latin and Greek were common languages, but they still used very technical terms. Neither terms were normal, household words used by the regular folks in the pews. They required an understanding of Aristolean metaphysics then, and they do so now.
Clearly, the Council considered it more beneficial to the Church to be very precise in the theological concepts, rather than making it understandable to 8 year olds.
So why fault the Church if it is still true today.
One other point, I don’t think there were many third graders who could describe what was meant by “One in Being”. Sure they could pronounce the words more easily than “consubstantial”, but I think the number who actually understood it was very, very small.
At least with 'Consubstantial", most third graders would recognize that they do NOT understand it, and this is a great opportunity for their parents, pastors or religious teachers to explain the concept to them. With “One in Being”, most never would have even asked.