Um, here's a quote from the article.
"Such practices infiltrated the Christian church after Christianity became the official religion of the Roman Empire in the fourth century."
It's prior to that point that people are asking for proof of the practice from.
Okay. Show me the orthodox Christian theologians or others condemning the introduction of veneration of the saints in the Fourth Century.
Hint: There aren’t any, because veneration of the saints was not introduced in the Fourth Century and it wasn’t contrary to the Faith.
YOUR theory is that a majorly heretical, idolatrous practice swept through Christianity in the Fourth Century, and NOBODY NOTICED UNTIL the SIXTEENTH CENTURY.
How is it that this form of idolatry was introduced into Christianity in the Fourth Century, and nobody objected to it for another 1200 years?