Even with the buff Hysteria has a few advantages over Malice Beam - it's still the stronger weapon of the two, arguably. If it turns out hysteria needs a buff, it'll get one, eventually.
Also, general statement,
Please guys, stop going "why x not y" between weapons that aren't top of their class to begin with. The aim isn't to balance B-tier weapons with each other, we don't want the myth food you have to be balanced with each other.
Simply put, currently, phys is meta and every type has a few weapons that are very good and a majority that are useless. Goal is to bring that useless majority up to par bit by bit while creating a meta where all types of builds are perfectly viable for #1. if you're going to compare items of that majority, we'll never get anywhere 😛