That this council mandated relics placed underneath altars of all Catholic churches in the eighth century in no way makes such actions nor the requirement of such a "Christian" practice. The Catholic church mandated many things that were nowhere found within the early church of the Apostles' lives nor of that even a few centuries later. What we DO know is that, even in the Apostles' days, there were wolves creeping in to scatter the flock. That superstitions crept in along with them should be no surprise. It is beyond question that the early church did NOT call upon martyred saints, nor worship them, much less presume their remains were imbued with supernatural powers so that they had to be preserved under altars. Worldly pagan ideals crept into the church and were absorbed in the idea that more souls could be converted. It didn't take long before many of the pagan practices became absorbed and then embedded too deeply to be purified out of Christianity.
We know from the book of Acts that neither St. Stephen, the first Christian martyr, nor St. James, who was killed by Herod, were invoked by the Apostolic church in any manner, because, if they had been, there would have been mention of such an important matter seeing as other events of less importance were mentioned. If such a practice was in conformity with the Apostolic doctrine, it would have been brought forward in the epistles of St. Paul and the other Apostles, yet there is nothing said about it. Even in the writings of the early church fathers such as Clement and Polycarp, there is nothing spoken about invoking the aid or intercession of the saints. It is always to God that believers are encouraged to pray to so that, if they are found in the same circumstances as the martyrs, God may grant them faith, peace, patience, wisdom and strength. So we know that this was a later innovation and not something taught by the Apostles.
It's interesting that you mention the martyrdom of Polycarp because the believers of whom he was bishop, rather than take up his remains to venerate, said in an epistle which was issued by the church of Smryna states:
Even in the fourth century, the orthodox Christians considered worship of every created being as idolatry. Polycarp's remains were treated respectfully and buried and the date of his martyrdom marked and remembered for the edification of other Christians. It did not mean, however, that they gathered his bones to venerate or to place them somewhere where he could protect them or provide some kind of power.
In the same book, Calvin had this to say about Marian devotion and relics:
This http://beggarsallreformation.blogspot.com/search?q=relics article goes into further detail about the many ways faithful Christians have been hoodwinked and fooled out of their money and, sadly, of their faith, when scams are discovered. So-called relic "miracles" were counterfeited and the devil laughed at the gullibility and vain seeking for signs. Calvin puts it well:
You may want to read the above document further as it speaks about the origin of the veneration of relics and the superstitions, legends and myths that people who are actually weak in faith need to cling to for strength rather than through faith in Christ - who rewards those who diligently seek him and says that they are blessed who believe even when they don't see. It is not "girlish squeamishness" that compels me to speak, but a hatred of the false gospel that snares the unknowing into believing lies based upon tricks. We are better served by heeding the sacred Scriptures than the rationalizations of men.
As to the St. Polycarp story, it is clear that the Christian community wanted to preserve his relics.
You cannot expect every practice of the Early Church to be mentioned by St. Paul. The reference to the relic under the altar in the Apocalypse is there, -- you ignore it. The Epistles mention things that were controversial. Veneration of relics was not controversial, -- it was common to non-Christian as well, -as you yourselves discovered.
Mary Magdalene came to the tomb to do -- what exactly in your opinion?