TheInfamousKira
Reseterror Resettler
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it's only been demo material from the Nibelheim flashback, yeah? In which case, Sephiroth's presence is in line with OG. Sure, they've definitely expanded that segment, stretching into excess may be one of Remake's overall project problems, but again, I think you're overthinking it a little.
If your complaint is that he's shown off in promotional material too much, I'd again say it's the same part of the same portion of the original. If your complaint is that they're focusing TOO MUCH on the Nibelheim flashback prerelease, I'd also counter that it's just because it's the first area in the game. It's a safe spot to showcase gameplay mechanics without spoiling any substantial story beats while advertising their product.
Tangentially related, I was initially fearful of the progress/quality of Remake before it launched because they had what I thought was an unhealthy obsession showcasing Mako Reactor 1 in their marketing. The idea that they showed it off, had a bunch of internal development hell ending with Sony itself interjecting, I was afraid that it was an ill omen. Turns out, it was just the first area of the game.
I'm not berating you, though. I'm just throwing out things to mull over.