So Irenaesus and Tertullian are heretics for believing in the immortality of all souls??? Tertullian lived from 155-230AD. Irenaesus lived about the same time. And let's not forget the Apostle Creed of the 6th/7th century;
Did it ever occur to you that the eastern church fathers who gave you this material could have been the heretics?
First, Irenaeus did not believe in, or teach the immortality of the soul by nature. The Orthodox teaching on this has never changed.
Second, Tertullian was a heretic because he embraced Montanism which teaches, among other thing, that the prophesies of the Montanists supercede those of the Apostles. I would call that a heresy, big time. You need to get your facts straight, HD.
What Kolokotronis told you is the Orthodox doctrine, always has been and always will be, because even the people you mention as believing in the so-called "immortality" of the soul (by nature) admit that it is not. Even Platonists in the early Church (i.e. Clement of Alexandria) admitted that the soul is not immortal by nature, but by grface.
The immortality of the soul is not its nature (i.e. it is not created immortal) but it is given by God (grace). If God created immortal souls then we would be God. You will just have to do a little more Church Fathers studying before you get the whole picture.
The problem with Tertullian and others on the Latin side (the root of St. Augustine's error, the fillioque error, etc.) is that their misconceptions always started with the poor understanding of Greek, and these, in turn, (mis)led to doctrinal errors.