I don't think one should confuse repetive or even ritual with insincere.
Most JWs say a prayer before every meal which is essentially "Thanks God for our food" and will say this prayer literally 1000s of times. That doesn't mean it's not sincere and heartfelt.
So why the big deal about the Lord's Prayer becoming repetitive and by inference meaningless because it is said repeatedly.
By that reasoning we ought to all stop saying "I love you" to our spouse because after the first few times it is meaningless, repetitive and insincere.
Also I dont know any Christians who ONLY pray the Lord's Prayer without also using free, open, unscripted prayer. Infact the ratio is probably 100:1 Open prayer:Lords Prayer, which is surely what Jesus wanted.