Did you read what I wrote? Or did you misinterpret? It was at the Council that the two received the "DEATH NAIL" to them ever being considered Scripture. Those two books were removed and denounced and officially rejected at the Council of Nicea BECAUSE of Athanasius. Both Hermas and AoP were used by the Arian heretics.
However, for most to know, 2 major things came out of Nicea, the Nicene Creed and the first version of the Athanasian Creed.
You said:
Canon was discussed at Nicea. However, it was not confirmed at Nicea. Both Shepherd of Hermas and the Acts of Peter ended being held as Scripture at Nicea. It was the following councils that defined the canon, but Nicea was the beginning. This is why it is often referred to, though most don't delve deeply into the history. It's often best to mention it as you have, as a point of order.
I'm sorry if you misspoke or mistyped, but I did read what you wrote, and I think I understood what you wrote correctly, even if what you wrote was not what you meant.
I don't really want to go on with this, because it's a side issue. But I get frustrated when people make historical assertions (particularly on canonical questions) without evidence.
You haven't really established that canon was formally discussed at all at Nicea. Again, Athanasius only mentions the Shepherd in relation to its use by Eusebius of Nicomedia in defence of Arius (in 'Decrees'), and almost offhandedly mentions it as non canonical - there was certainly no discussion about its worth as a canonical book (in fact, given the earlier scepticism of the likes of Origen and Tertullian, it seems likely that by the fourth century there was some level of consensus that the Shepherd, while perhaps useful, was not apostolic nor canonical). Even then, it's striking to me that Athanasius still refutes Arianism on the basis of the text of the Shepherd, which would seem to make it odd to subsequently ban the book at the Council because of the Arian heresy - Athanasius seems to take the view that the Shepherd was not Arian nor gnostic, otherwise presumably he wouldn't bother to use arguments from it. Even then, there is still no evidence of an actual discussion on canonical or non-canonical books at the Council.
Worth noting, again, that neither Athanasius (in 'Decrees' or in his Easter letter), nor the Canons of Nicea, mention the Acts of Peter. In fact, I consider it highly doubtful that there was any one dominant Greek text titled 'Acts of Peter', mainly because most of the patristic references to Petrine traditions are non specific and most probably do not even refer to a written text - and the actual MSS are basically limited to the main seventh century Latin text usually identified with the Acts, a Coptic fragment of a possibly parallel, but not dependent or merely translated text, and fragmentary Greek crucifixion narratives, again not dependent on any of the other MSS.
If you have a source for Arian use of a definitive Acts of Peter, or for that matter the use of any non-canonical Petrine tradition at Nicea, I'd be interested in seeing it. Any official rejection by the Council of Hermas or AoP would be interesting as well.
Otherwise, I stand by what I originally said - there was no formal discussion of biblical canon at Nicea at all. What discussion there was (by Ath) was on the basis of Arian arguments from non canonical texts, and even then his approach seems primarily have been to show the arguments were wrong on their own terms, rather than circle-draw and exclude those arguments on canonical grounds (Ath elsewhere actually is quite positive towards the Shepherd, even if he denies it is an inspired text - 'Incarnation of the Word').
Otherwise, yes - the Nicene Creed, as a response to Arianism, was really the main thing to come out of Nicea of lasting historical significance. I'm sceptical of Athanasius actually writing the Athanasian Creed, mostly because he never mentions it or quotes from it in any of his writings, nor have I seen a source showing it being mentioned at any Council, but that is well and truly out of the park in terms of relevance.
