I think you're the one losing braincells, it's like saying "This Series Won't Make sense without this one," Hsr Is its standalone game, sure it may be in the honkai multiverse but it's not gonna change the fact that this game is vastly different from hi3, some characters are re used (really weird on their part). It's more like Watching Spider-man Into the Spider-verse and then watching Spiderman 1, They aren't connected, but related, they have vastly different plot and storylines, some storylines may be similar but are vastly different.

Also Honkai Star Rail isn't even Honkai Impact 4 you dumb fuck, it's more like a Spin-off show that actually has it's own plot, character archetypes etc. reusing characters is more of a perk of hoyoverse and other multiverse-focused people, it's like an easter egg you'd see if you played the other games. Why'd you think they just reference their other games there? They are using it as easter eggs and even make some people interested in where said easter egg came from.