Sephiroth can't go lightspeed anymore than he can hit someone with the power of an exploding star. Lulz. And people call me a fanboy. I'm pretty tame caompared to such outlandish, and entirely baseless claims. Both of which defy everything about FF7.
Remember that whole summoning a meteor and waiting a month thing Seph does in FF7? KIND OF MOOT if you can use the power of an exploding star! And that attack doesn't kill Cloud.. WAIT! Maybe Cloud is SUPAR DURABLEZ! He could just jump into space and tank the meteor hit for the planet at no damage. haermm Ohwait, no. Cloud would have been killed by Shin Bahumat if Aeris dead ass hadn't helped him.. WAIT! Maybe Bahumat was going easy on all that fragile metal scaffolding?
The "light speed" movement is a single, obviously hyperbolic and isolated statement which applies only to one, probably non-cannon special move in Dissidia. He doesn't move that fast. If he did, he wouldn't need to pilot a plane-Ohhh waaait. Wasn't that one of those big plans he had? You only need to go mach 22 to escape the gravity of a planet, and he couldn't even do that. 😬 Cloud can react to Sephiroth's movements, Cloud is OBVIOUSLY FASTER THAN LIGHT! Ohwait, Cloud gets shot in AC. Hm. MAYBE THE BULLET WAS FTL!?
...No, FFanboys. No.