All Marian titles are capable of being misunderstood, even ancient and unquestionably orthodox ones like "Theotokos" and "Mother of God". While I personally believe that Mary is Co-Redemptrix in the sense that this has traditionally been taught by Catholics, I have no problem with those who do not want to see this made a dogma due to the potential for misunderstanding. One of the characteristics of the current Crisis is poverty of catechesis such that many, possibly most, do not properly understand the dogmas which we already have. I see it as legitimate to be concerned about adding a new dogma at this time.
But that was not the case against the title Francis made in his most recent comments on this topic.
He continued: “It is true that Christian piety has always given her beautiful titles, as a child gives his or her mamma: how many beautiful things children say about their mamma whom they love so much! How many beautiful things.” “But we need to be careful: the things the Church, the saints, say about her, beautiful things, about Mary, subtract nothing from Christ’s sole Redemption. He is the only Redeemer. They are expressions of love like a child for his or her mamma — some are exaggerated. But love, as we know, always makes us exaggerate things, but out of love.”
He is not saying this title is true but might be misunderstood. He is denying that it is true. He dismisses all the past teaching on it as pious exaggerations. Furthermore, he implies that this applies to all Marian titles. Historically, heretics have falsely accused us of making Mary into a goddess by giving her the title "Mother of God". (Anyone who knows the history of this title knows how blatantly untrue the accusation is.) So when Francis said that Jesus entrusted Mary to us " as a Mother, not as a goddess, not as co-redeemer"he was subtly supporting this accusation.
There is a reasonable case to be made against creating a new dogma, but this is not what Francis was doing. He was essentially attacking all Marian devotion as based on exaggeration rather than truth.