the only kinda good written react fic I've read is the one where the 30k emperor and the primarchs react to if the emperor had a text to speech device, and even that has the "too many people" problem, yeah, so most of the primarchs end up being on rotation.

character react content is better when its a video, because it feels like your watching along with the characters being played, while written stuff has to deal with scribing out the content being reacted to.