In what year or era did Mariology become excessive and overindulgent?
Robert Sungenis traces it to the first centuries: once Mary was called the Mother of God, some went on to raise her to almost God-like status. He points to Renaissance paintings that make Mary the center of Pentecost, where Scripture gives her no part, and says such excesses will always be with us.
Sermons that focus on Mary's power to crush the serpent plus an essay and a podcast proclaiming the Reign of Mary are excessive in my opinion. Two contemporary sources about the Reign of Mary: "Grace of Contrition and the Reign of Mary" at Tradition In Action [https://www.traditioninaction.org/religious/c002rp.htm]; and In The Spirit of Chartres Committee's podcast by Edmond Dantes titled, "The Reign of Mary" [https://www.youtube.com/@ISOC-Live/podcasts] I'm interested in period when this hyper-attention to Mary appeared in sermons and books? I'm guessing that we have the Protestant Reformation to blame in which the Church saw the need for a deeper devotion for the faithful. You know what I mean? We pray the Rosary every day so I have a devotion to Our Lady. We own both Montfort's books. But when I hear an entire sermon focussed on Mary, I find myself tuning out. The Church is experiencing Her Passion, Satan is Unleashed, and we need more sermons on Jesus. God bless.
Answer
It started in the first centuries when Mary was called "The Mother of God" and not merely Mother of Jesus' human nature. From this, some elevated Mary to almost God-like status. For example, if you look at paintings of Pentecost from Catholic Rennaissance painters, it shows Mary as the central focus of the Holy Spirit's descent at Pentecost; but according to Scripture, Mary has no part in Pentecost. The visions of Mary in later church history (LaSallete, Akita, Fatima) show the prominence of Mary in eschatology, and that God is using Mary to usher in the end of the world. But the excesses will always be there. That is just the nature of the issue, so get used to it.