That is not the foundation of that belief.
Mary heard the Word of God and obeyed, that is why she was blessed to be the Mother of our Lord. She was chosen for Him because she was blessed, but the other way around.
No one, not a one, not one single Catholic has ever claimed that Mary is greater than Jesus.
That is a distortion of the doctrine and a gross misunderstanding of it results from such distortion.
Where did I insinuate they did? I did not. That post showed that Jesus considered all who believed were to be considered more blessed then Mary. “Yea rather, blessed are they that hear the word of God, and keep it.”
He also said that other then Him there was no one greater then John the Baptist, not even Mary.