I've been meaning to try to make some Fate/Zero-ish epic music when I got back to music production (and since that's now, I guess maybe that'll be soon) but I haven't messed with it much.
I have a few suggestions though without going super in-depth or anything (and do keep in mind that I'm far from a pro myself).
The first suggestion had me dig up this video that I saw some years ago. I think you could really iterate on the rhythms of your melodies to spice them up. It'll make a big difference. The instruments all feel like they're doing their assigned thing but they could be spiced up and I really think the way to do that here would be to chop up your rhythm some and mess around with it a bit. Don't be afraid to really vary things up. You can always put them back after if you feel like it doesn't work.
The second tip is something I feel like I've heard a lot from other musicians going back to the first time I heard it in college and that is basically to have a mix of simple and complex. Not too much of either. And by complex I don't mean something super technical but if you have a melody that really pops, then the backing instrumentals or percussion or whatever else can be simpler to emphasize it. A bit of mixing aptitude can help with this too but what I think you could do is pick an instrument in your composition and add some layers to what it's doing. Let the other simpler parts of the song be the basic foundation that elevates those one or maybe two really interesting parts. And the parts that jump out don't have to be the same instrument for the whole song. You could alternate the points of interest.
Now, I feel like there's an instrument here that flirts with that whole idea and that's the guitar. At 22 seconds and again at 44 seconds, it really feels like the guitar is ready to really capture the listener's attention but it's brief. I really like those parts though. I'm not saying to 'make the whole song like this or that part' but I think those parts really work and it's because there's some interesting instrumental bit that jumps out unexpectedly and captures my attention. It's doing something different for that moment and I can't help but focus on it. So when you're composing I would suggest trying to decide which instruments have the supporting part and which have the lead part in each section. If every part is just going crazy then it'll sound pretty messy but if every part is just playing its own assigned role and everything feels expected, then the song will just sound too safe.
Also, this isn't really specific to the song but I really love studying music theory and I feel like it really helps a lot with my composition. I've bought my share of theory books and Udemy courses on music theory and FL Studio and whatnot but I'm sure there are also some great YouTube series that teach music theory from basic to advance if you aren't already studying.
Oh, and just like with art, find references. Like if you want to write epic orchestral sounding music, find that in movies or anime or video games or on Spotify. Where ever. Like if you like big orchestral pieces with maybe some more modern sounding guitar mixed in, listen to Fate/Zero's OST for example. There are a few examples below. And really focus on the instruments. Think about which ones are driving the piece and grabbing interest in a given moment and which ones are supporting. It might not be the same throughout a whole song.
Track 1
Track 2
EDIT: also the simple/complex thing can apply to parts of a song too. Like if the verses are more complex, the chorus can be simpler. If your chorus is busy, your bridge can ease things up before going back into the chorus again. There's rhythm to composition.
