Hello, all. As you know, I do not believe that there is a "normal" Angel class, and believe that Seraphim are the general Angels. There isn't any evidence suggesting that there is a separate "normal" Angel class, so there is no reason we should assume that there is. I took the liberty of going through the debate that we had a few months ago, and wrote down all of the arguments that you presented. Here are all the reasons that you said you believe that there was a separate "normal" Angel class, and here is my current argument against them, showing that there is no 'normal' Angel class.
1. Different power levels
The main reason that you said you believe that Seraphim were different from "common" angels is because Angels like Zachariah and Naomi seem much more powerful than Angels like Inias and Samandriel.
All (non-knight of hell) black eyed demons are the same rank/level as each other, but their power levels vary from demon to demon. For instance Meg, a black eyed demon, is much more powerful than Gerald, also a black eyed demon. It is the same thing with Angels. The power level varies from Angel to Angel, so some Angels are much more powerful than others. However, this does not indicate that they are a separate class of Angel. Zachariah was Castiel's superior, and was more powerful than him, but this does not mean that he was a separate class than him.
2. New and Improved Castiel
Another reason that you said you believe that there was a "common" Angel class was that God brought back Castiel "New and Improved".
Before his death, Castiel was essentially human. He had no wings, was fallen from Heaven, and lost all of his powers. After God resurrected him, he gained his wings, status, and powers back. He was brought back new and improved, as he got all of those things back. While there is nothing to suggest he was brought back as a different class than before, it is possible that God resurrected him as more powerful than before. As said in argument one, all Angels have different power levels, so new and improved only means that his power level was improved from before, not that he is a separate class of Angel.
3. Faster smighting
Another argument that I have seen about this topic is that Seraphim smight faster and easier than "normal" Angels.
The change in the smighting effect started in season 6, and happened with all Angels, not just the higher-tier ones. This was just a change in the effect, and isn't separating the classes of Angels.
4. Special introduction
Another argument that you presented that Seraphim are not the general Angel class is that Castiel referred to himself as a seraph, where no other Angel has.
Angel is a general term, and most celestial beings refer to themselves as Angels, not their specific class. For example, when Lucifer was talking to Nick, he referred to himself as an angel, not an archangel. Also, out of all the times that Castiel has referred to his species, only one time has he said Seraph. This shows that it isn't common for an angel to refer to itself as its specific class.
5. Archangel>Seraph>Cherub
In "My Bloody Valentine", Castiel said, "What people have mistaken as a Cupid is actually a lower order of Angel. Technically it's a Cherub, third class."
This quote has 3 possible meanings
a. Castiel was using "3rd class" as a metaphor for "lower class"
b. Castiel was saying that Cupids are the 3rd class of Cherubim
c. Castiel was saying that Cherubim are the 3rd Angel class
Here are the problems with each of these options.
a. First off, in the earlier seasons with Castiel, he rarely, if ever used metaphors or talked in slang. He almost always, if not always talked literally, so the chances that he was talking in a metaphor are pretty low. Also, Castiel already mentioned that they are a lower class of Angel, so why would he say it again? That would be pointless. His first sentence (what people have mistaken for a Cupid is actually a lower order of Angel) is more general, where as (technically it's a Cherub, third class) is a more in depth, detailed description of them, so he was speaking literally.
b. I used to believe this interpretation of the quote, until I saw the error in its logic. Castiel said that humans mistook Cheribum for Cupids, so that means that Cupids aren't real, but are just a made up name for Cheribum. This interpretation is saying that Cupids are a class of Cherub, where as Castiel tells us that Cupids are just misinterpretations of Cherubim. This interpretation of the quote goes against what Castiel is telling us.
c. The other two interpretations have been shown to be very unlikely and/or shown to contradict what Castiel was saying. This interpretation is the most likely, and shows that Cherubim are the third class of Angel. As archangels are the first class of Angels, this only leaves room for one other class of Angels (seraphim).
With this, I have shown that there is no evidence suggesting that there is a "common" Angel class, and that Castiel's quote shows that there is no room for one. In conclusion, all of the evidence shows that there is no "common" Angel class, and Seraphim are the general Angels.