I was not responding to you. My apologies for the confusion. I also did not mean to shut that person down by making it clear that their position was the ancient heresy known as modalism (which was condemned both by the Arians and the Nicene party), but to make people aware of the fact that their view is not the view of Nicene Christianity.
As I already explained, the Apostles' Creed is not earlier. The Old Roman Creed is, but the purpose of the Old Roman Creed was to exclude pagans from the baptismal rite, whereas the purpose of the Visigothic "Apostles'" Creed was to include both Arians and Catholics.
The historical focus has always been on Arius because he was the chief proponent of the view that the Son is not God together with the Father, but was the first of all created beings. Your original question, regarding the meaning of words in the Nicene Creed, must touch on Arius because that wording was put in there specifically to condemn his position. Of course Arius was part of a broader theological movement, but the issue at hand- the wording and meaning of the Nicene Symbol- is specifically the issue of Arius' different interpretation of "eternal" and "begotten." You cannot discuss one without reference to the other.
Certainly there was more theological and liturgical variety in the early church than the forms of belief and practice that were codified at Nicea and in the subsequent councils. And of course there was theological development.
However, my point was that everyone at the council came from churches in which Jesus had been worshiped as God as long as anyone could remember. The excellent work on apostolic christology by Larry Hurtado is just one good example of a whole field of contemporary christological studies confirming what everyone, Arius included, at Nicea knew.
My point was not that this was necessarily true everywhere (the Ebionites, for example, were a divergent faction in the early church that probably did not worship Jesus as God), but that Arius, in his sincere desire to show that he was orthodox (his whole point, after all, was to combat modalism, a belief everyone agreed was heretical), conceded that Jesus had always been worshiped as God in the church. If you actually read his own writings and the writings of later Arians, you can see that they are all willing to concede that from the perspective of worship, they were willing to call Jesus "God" because they accepted this universal practice of the non-gnostic, non-modalistic, non-Montanist church (i.e., the Catholic Church, as far as both Arius and his opponents were concerned).
Now, this goes back to my original point: both Arius and his opponents, particularly Hilary of Poitiers and Alexander of Alexandria (Athanasius would only write after Arius' death against later Arians who had at that point received imperial patronage because Arianism was a particularly attractive to justify supreme earthy authority- more on that later if it comes up) agreed on a certain existing framework of praxis within which they defined their theology. This does not mean this was always the case in every place, but it does mean that when it comes to understanding the meaning of 'eternal,' 'generated,' and 'homoousious' within the context of the Arian-Nicene controversy, we are working within an agreed-upon framework that is monotheistic, anti-modalist, and worships Jesus of Nazareth as God.
By Cyril's time (active 412-444), after the Council of Constantinople in 381, the formulate "eternally begotten of the Father" was universally agreed upon and a basic criteria for having full civil rights and liberties within the empire. The Arians were at that point largely confined to Gothic populations moving westward across northern Europe, having been converted by Wulfila, and Arian bishop supported by the Arian emperors of the mid-fourth century. Cyril lived in a time in which Augustine in the west and the Cappadocian fathers in the east had made it very clear what they meant by "eternally begotten of the Father" (and they agreed on this point).
To be a heretic is to expressly deny the truths expressed in the ecumenical creeds, so while I would identify people's beliefs as modalist or Arian, I would not accuse them of heresy unless they publicly denied what the church catholic has professed, in accordance with the Scriptures, since antiquity.