Well, Christ said “when two or more are gathered in my name…”. Hence it is safe to assume that having more than just ourselves praying for something is beneficial.
It is also logical. If one accepts the fact that individual prayers to God are beneficial, one has to accept the fact that other prayers to God are also beneficial in an additive manner. So it is completely logical to ask others to pray for our intentions. The final step in the logic is that the same logic applies to the saints and angels,we should also ask for their prayers.
I appreciate your thought. But here’s the problem: If that were ALL Jesus said on prayer, you might have a stronger point. But he also said, “when you pray, go into your room, close the door and pray to your Father, who is unseen. Then your Father, who sees what is done in secret, will reward you.” That sounds to me like someone praying alone. So which does Jesus want? The Bible is full of those sorts of differences, and they make the construction of specific doctrines on any one thing found in the Bible pretty difficult and contentious (see the history of Christianity for more on that).
As to the rest of your logic, it’s not at all proven that if one prayer is good, more than one is better. If I utter one sincere prayer, and God hears it, what’s to be gained by piling on? There’s no clear connection whatever to the idea that “other prayers to God are also beneficial in an additive manner.” --as if God is sitting there waiting until they reach critical mass or some magic number. When is enough enough? Is it sufficient that three people in our parish pray the St. Michael prayer? Fourteen? Seven hundred?
We have no evidence about the mechanism of prayer, and Jesus himself gives us ambiguous advice on it. But it seems to me that it can’t be like, say, accomplishing a task such as raking leaves or pushing a stalled car. In those cases, the more people you get involved, the more quickly and easily the task will be accomplished. It doesn’t seem accurate to map that, analogically speaking, to the idea of prayer, which is an infinitely more subtle undertaking.
I know the Church teaches otherwise. It doesn’t make sense to me, but I realize my feelings on it don’t mean much.