Let's have a little history lesson on prayers and on vain repetitions. First vain repetitions:
Focus on “vain”. The heathen were not praying to God, but to carvings of idols…all in vain as wood and stone engravings can do nothing and thus all such prayers are in vain. There is at least one Old Testament story about this, how wooden/stone images could do nothing, but God could—and did.
Jews--and Jesus--did recite repetitive prayers.
The 150 Psalms come to mind. Some Jews did/do pray all 150 of these Psalms daily, weekly, monthly. The Psalms themselves are often repetitive. Psalm 136 said at Passover repeats the same line again and again. So did other Psalms Jesus was praying on the cross. Remember Jesus' parable about the persistent widow and the instructions not to stop praying.
The 150 prayers of the Rosary came about because in the early Church not many had copies of all 150 Psalms. The Psalms are a great meditation for meditation on God's great works in Old Testament Times. The Rosary was used as background as people focused/meditated on events in the life of Jesus as told by the New Testament Gospels.
Shadrach, Meshach, and Abednego in the Book of Daniel use repetitive prayer while in the fiery furnace.
Repetitive Prayer in heaven - Reference the Book of Revelation...
Revelation 4:8-11 “The four living creatures … day and night … never cease to sing, “Holy, holy, holy, is the Lord God Almighty, who was and is and is to come!”
And whenever the living creatures sing these praises, the twenty-four elders around God’s throne in Heaven also fall down before him … singing, ‘Worthy are you, our Lord and God, to receive glory and honor and power, for you did create all things, and by your will they existed and were created.’
Now let's address praying to/with Mary and the Saints in Revelation 5:8...
“The twenty-four elders fell down before the Lamb, each … with golden bowls full of incense, which are the prayers of the saints.”
Note the twenty-four elders and the saints do not answer prayers, but take them before the Lord.