There's other benefits to a mass claim.
A mass claim with a decent ordering can catch scum inadvertantly in a lie about what they did at night. Sometimes night actions contradict each other and you can lynch based on that info. I've seen that happen a lot. Sometimes people can corroborate each other's stories about night actions and you know that they are either both lying or both telling the truth.
As a for instance, say there is a doctor and a redirector. Pretty reasonable, considering we saw one night kill fail and when we think scum probably expected it to go through and we saw another night kill hit a person we don't think scum was trying to shoot.
Well, the doctor can claim who they protected N2, and we probably shouldn't lynch that person. Then the redirector can claim which person they protected by redirecting onto gkrieg, and we shouldn't lynch that person. And if the redirector and doctor are both townie claims and consistent with other people's claims, we know they are not fake claims.
Or, if they get counter claimed, we can sort that out and lynch between them if we don't think there are two doctors.
This is why I said that my best scum read for now is Galzria. I think it's an OK shot at being correct, but I'd much rather lynch with all the information that may come out with a mass claim instead. I'm not confident enough on Galzria at all. I don't see how anyone can be confident enough about their top scum read to not want the extra information we'll get from a mass claim.
As far as scum knowing who to shoot, it's not really that simple. Say just the redirector claims his targets. Then, scum will just shoot the redirector, and maybe if there's a doctor he'll be protected. But if everyone claims, town as well as scum may know better who to target with their PRs. We may be able to coordinate at night to either expose scum or protect important PRs. There's a lot of potential that we just don't really know about until we try it.