Yes, Jesus absolutely has made a promise on how a prayer is supposed to work. But, since the prayer doesn't work, Christians came up with all sorts of 'definitions' where the text doesn't mean what it says.
Mark 11:24 Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours.
Well, lets see. This text, very conveniently for Christians, doesn't apply to modern Christians when they pray for anything that ends up failing. But, when a Christian, who gets sick with incurable illness, gets healed, then, voila, Mark 11:24 is literal again and surely does apply to modern Christians.
Clearly your position makes perfect sense. That's the position I would have taken too, had I remained a Christian.