Big controversial opinion coming up, but, Duel of the Fates....was not darth maul's theme.
It had a specific purpose in the prequels, based on the time I've heard it. Once, in the darth maul fight, obviously, where, who lived or died would decide the fate of anakin. Second, in attack of the clones, when anakin rushes to save shmi, where her death would push anakin to the dark side. A third time, in revenge of the sith, when yoda battles sidious, who holds such fate over anakin.
The thing is, whats lost on using this theme for darth maul, is that, he would absolutely want this to be his theme. Maybe they're silly lego specials, but those properties where he sings it may be accurate to that desire. Maybe its a headcanon or me playing death of the author, but I think maul would want to claim this theme because he wants to have a role in fate.
The one theme we know was designed specifically for him, is in rebels. A subtle tune. One that sticks in the shadows. The notes progress higher and higher, but go back down slightly. The tune after, feels unsure. The more we hear this, the sadder Kevin Kiner makes it sound. The tune never really amounts to anything.
And I think shadow lord could have absolutely added to this--if not for the marketing. Because in the first episode, we hear duel of the fates play, more loudly and bombastic than we've ever heard(thank the current state of cinematic music smh), and its when we don't know very much about him. Skip ahead to episode 8, he's in the tunnel, he cries, but then he puts the mask back on, and when he stands up, you can hear the theme play, albeit in a blink and you'll miss it way. I really wish this was more expanded on. The marketing kind of makes it fall apart, because it absolutely used the song as just "the darth maul aura farm song"
I just thought this revelation was really interesting. There's a gap between who he wants to be, and who he is, or you could even argue, who he knows himself to be.