Anyone that would present themselves before the King and stand there and repeat something over and over 100 times in a row is behaving foolishly and is insulting the King, and would not derive any spiritual benefit from it at all except some egotistical profit, which is evil.
Eccl 5:1 Guard your steps as you go to the house of God and draw near to listen rather than to offer the sacrifice of fools; for they do not know they are doing evil.
Eccl 5:2 Do not be hasty in word or impulsive in thought to bring up a matter in the presence of God. For God is in heaven and you are on the earth; therefore let your words be few.
Eccl 5:3 For the dream comes through much effort and the voice of a fool through many words.
If it were condemned, why did Christ do it?
Matthew 26
39 And He went a little beyond
them, and fell on His face and prayed, saying, “My Father, if it is possible, let this cup pass from Me; yet not as I will, but as You will.” 40 And He came to the disciples and found them sleeping, and said to Peter, “So, you
men could not keep watch with Me for one hour? 41 Keep watching and praying that you may not enter into temptation; the spirit is willing, but the flesh is weak.” 42 He went away again a second time and prayed, saying, “My Father, if this cannot pass away unless I drink it, Your will be done.” 43 Again He came and found them sleeping, for their eyes were heavy. 44 And He left them again, and went away and
prayed a third time, saying the same thing once more.
There are certainly vain prayers. Prayers can be empty and vain, whether they are repeated or made up on the spot. But by the same token, just because something is repeated does not make it vain.
Do you think praying the Psalms is evil?
And as far as repetition, if a man tells his wife every day that he loves her, does that make it vain and false?
We should use wisdom in discerning such things. Sometimes people criticize what they don't understand, because they make assumptions about it. But if it is not their practice, they often have no idea what they are really talking about.