The argument on your side is they can't do this unless they have all power and all knowledge.
But we're not talking about the saints knowing everything and being able to anything that can be done. We're talking about doing a few particular things.
Having the power or knowledge to do a few things, is not having the power to know or do all things.
There is a distinction between asking someone who is living on this planet at the same time as we are, with whom we can communicate in a normal fashions using words, vs praying to someone who has died and left the physical plane of this existence.
What exactly is that distinction? We rely on the Spirit in any case. We think the koinonia in the body of Christ is stronger and more important than death. We think the koinonia of the Holy Ghost more real, more vital, more important than any other. We think the Holy Ghost, the Spirit of the Word carries communication far better than vibrtions in the air or marks on paper.
We have been forbidden by God to contact the dead
Before the Incarnation and all that followed.
The point is very similar to the point of asking sinners on earth to pray for your needs. When I have a need, I ask my friends to pray. When I have a joy I ask my friends to share it with me.
Not all my friends have died. Some of them have. But nearly all my Christian friends have died with Christ and now live in His life. That death and that life are stronger and more real than the death of the body.
I don’t see any indication anywhere in the NT that indicates that we are to pray to those who have died and left this planet and stage of their existence.
Jesus taught us to pray to the Father. If it’s good enough for Him, it’s good enough for me.