It has been established that Amathaon is the Kuriotates' patron, and that Eurabatres is his creation.
On the Mana chart, Creation is the opposite of Entropy. Thus, "the Enemy" is probably Agares. "The Taint of the Enemy" would be any form of corruption. It wouldn't just be following the Ashen Veil, which probably hadn't been founded yet. The most common taint is almost certainly Greed, as most mortals who wind up in hell go to Mammon's hell. Keep in mind though that it was Agares who managed to corrupt the other evil gods, so their "taint" would ultimately be his too.
It would seem that a mind free of the taint would mean that Cardith was a sinless being. However, it was also been stated that the Agares taint was so pervasive that it touched all of Creation, and nothing in creation would survive if The One lashed out to destroy the taint. That is why The One has not returned, out of mercy for those who, he created. Although suppose it is theoretically possible (in Erebus) for a faultless being to be born in a faulty world, I just got tho thinking. Wouldn't Eurabatres, Amathaon, and all the good gods also bear the taint in some degree? Does that mean that if Cardith was faultless, the merger with Euabatres introduced a slight corruption?
I'm pretty sure that Kael has said that "the most powerful creature of the created" actually mean that he is the strongest being created by anyone expect The One. This would actually imply that Eurabatres is stronger than any archangel, or even than the current God of Nature.
It does seem odd that the gentle god of butterflies would also create the strongest and most destructive being in creation. Maybe he thought that such a creation would be able to restore peace most quickly?
I'd like to think that Angels and Dragons are more than other soulless creations. The only way I can see to explain them having The Divine Spark though is to say that the god who created them did not merely form them from their aspect, but from their very soul. Every angel and dragon would then have its own divine spark, but not necessarily one of the same nature as a human would. (This would also mean that Dwarves have souls formed from Kilmorph's, but their souls are of the same nature as her angels rather than humanity.)
Since the god's power is not infinite, he loses much of it with ever he makes a creature with a soul. This means that the stronger the creation, the weaker the creator becomes. I think this fits the FfH mythology quite well. Sucellus was generally considered to be the weak (especially by Basium), but his archangel was the strongest of them all. This would mean that Sucellus used more of his own divine spawk to form Sucellus than the other gods used to form their archangels. It would also mean that Agare, who never created an angel, is definitely the strongest of the gods. Since Eurabatres is greater than any archangel, Amathaon probably has the least power left with which to fight. He could have created Eurabatres so that he could personally remain gentle and uninvolved, but have his creations defend him. Sucellus was also considered to be uninvolved in the godswar, but his archangel was extremely active, even attacking Agares directly.
I'm also thinking that splitting a soul like that could happen "asymmetrically," causing the god's personality and that of the archangel to become quite different, but still exemplify their aspect. A god could have tried to preserve qualities (like gentleness) that he liked in himself and so kept those qualities while putting the other aspects of himself into his creations, he could have specifically tried to give his creations the qualities most needed to help him fight the godswar (thus leaving himself deficient in those qualities), it could have been completely uncontrolled, or it could have been sunconcious. If this is the case, Amathaon could be the gentlest god specifically because he created the greatest beast of destruction that Creation has ever seen. The same would be true of Sucellus and Cernunnos, but to a lesser extent. It could also mean that Arawn's unwillingness to get involved in creation is the result of creating Basium (and Gyra, but she isn't nearly as different from Arawn as Basium is). (Despite having two precepts, when Arawn created two archangels from his own soul he may have become one of the weakest gods.)
I am also of the opinion that Os-Gabella must have a soul, since she is so good at magic. I suppose that it is possible that each god gave her a small fragment of his, but I prefer to think that she and Nemed were once one. She would thus essentially be his archangel, but this would be the only case where the split was actually 50-50. It could be that Nemed specifically tried to preserve his identity when this happened, making sure that he held onto the traits that he liked best in himself and for which the other gods respected him. However, non even a god has such a one dimensional personality, at least once his soul is freed to multiple aspects of creation. Thus, his darker side was all that was left for Gabella. Selflessness was a core part of his personality, but there was still enough of an ego to not want to sacrifice self sacrifice. He wouldn't recognize himself without goodwill, and so wouldn't sacrifice this part of self sacrifice. Without this, his other half still possessed a willingness to give up her very being (as shown both his his willingness to give up godhood and her quest for suicide), but that was twisted into both Sadism and Masochism. Thus, the desire to be Good (and especially to be able to consider oneself good) created Evil, and may have doomed us all. That may be an odd moral to convey, but I think it fits quite well in a dark fantasy like FfH, where Balance is valued over any extreme.