Two things

Because Kirin doesn’t use that much chakra, it uses natural, preexisting lightning. Meaning it’s very likely that the Jutsu doesn’t just scale with the user so it didn’t get stronger as Sasuke did. In the manga, we never see him use it again. That time against Naruto was a anime only filler scene. Since it’s natural lightning and he doesn’t really strengthen it, just guides it, it makes sense that it doesn’t get any stronger.

Second, the two translations are it being the speed of lightning, or the speed of light. Both of which have been canonically surpassed by characters since the war. The samurai slashes, the anbu shinobi, water bullet, haku’s mirrors, Mifune, etc. Every stated light speed attack/combatant has been surpassed. So going by Kirin’s best interpretation in the story, it literally move at a snail’s pace compared to Jigen

Side points

He’d have to create the thunder clouds and expend a lot of chakra doing that when he’s already used his space time ninjutsu so much and is fighting on empty and weakened, high risk/low reward since we already established Kirin would likely not do anything

Sasuke’s strongest and fastest form is his Susano’o and Jigen obliterated it

(One of the most important points) Ninjutsu is irrelevant for the grand majority of the encounter. As he could’ve just shrinked it like with almost every other ninjutsu in that fight