Will it? At least instances can defederate, although as we're seeing, unless instances are very small, admins are proving reluctant to use the nuclear option.

I have hope that as Lemmy matures, admin tools will get better and more granular - like options to defederate communities and not whole instances.

Reddit has no motivation to improve in this area, and they won't, until it's too late.

Fediverse is mostly open source. So anyone can implement anti-spam mechanism to their instance. Although it is currently open to spam, I think it will be much more spam-proof if it becomes mainstream.