Almost every time the word "saints" is used in Scripture it refers to the living, not the dead. So the angels are offering our prayers, not the prayers of dead people.
There is no doubt that those in heaven are in a different space, dimension, time, and etc. but you still have not shown that those dead in Christ can hear our prayers.
As to what the early church taught that is not the issue since you cannot show those in the early church received this teaching directly from any Apostle.
hear our prayers.