I get what you are saying, but again, I have never seen anyone use "epic" as a "relative term," and that just seems strange to me. I kind of get where you are coming from if you use "epic" as an adjective (e.g. "that song is epic" (either referring to length or quality), but it makes no sense as a noun (e.g. "that song is an epic."). But I do note that you seem to mix the two uses together, so I am still at a bit of a loss.
And, yes, I would consider Shogun an epic if Dream Theater wrote it. But we could throw around examples all day of songs that are somewhat..."borderline," for lack of a better description. As I myself have said, and as I think most would agree, there is no set criteria for what constitutes an epic, and the lines quite often are blurry. I can't take a hard position that a song is or is not an epic, and I am not calling you (or anyone else) wrong for disagreeing with me. Again, my only issue is just that I find it weird that you seem to refer to "epic" as relative. But anyway, no need to go too far afield with this.
Not to get too far afield either, but I do want to quickly clarify my stance here, because I actually think we agree and just are miscommunicating. What I'm saying is that the noun "an epic" actually
should be a fixed term in the ideal, but it tends to get
used in a relative context, which is what creates confusion, especially when it comes to a band so far out of the length/structural norms as Dream Theater.
I think that most songs over, say, nine minutes (arbitrary but reasonable cutoff, I think) are epics, unless they are strictly just a standard verse-chorus-verse-chorus-break-verse-chorus structure where the break is just aimless jamming that
happens to be long, like, say, In-A-Gadda-Da-Vida or something. Occasionally, shorter songs that have particularly expansive arrangements (like TKH, for example) can fall into the category as well.
Obviously, that classification encompasses a good portion of DT's discography, and I do think that the songs that meet those criteria are epics. period. However, the term is clearly not typically used that way on this board, and I think that's because given what DT does, it wouldn't provide much distinction. Voices, Beyond This Life, In The Name of God, and Octavarium are all epics, but their scopes are very different, so lumping them all under the "epic" umbrella is a rather unhelpful characterization. So applying the term "correctly" would result in the term actually losing its meaning a fair bit; thus we tend to move the line of "epic" to the songs that are "especially epic" (TCOT+, basically). Then, you hear the term "mini-epic" thrown around to describe songs that would be "epics" by the Triviums or radio-ready rock/metal groups of the world. As such, I think that when it comes to stuff like ANTR, we tend to emphasize what
isn't epic about it, just to distinguish it from the ACOS group. And thus we get different criteria for use of the word "epic" with DT songs, just to categorize more finely, when in the larger context, many of the songs we don't think of as "epics" actually do qualify, and rather easily at that.
Just my two cents.