Sadly yeah. We absolutely should use email signup because it filters our the absolute lowest effort bots, but it does nothing against higher quality bots or humans. Not only can you easily spin up new emails on the fly, but many emails allow ways to make the email appear unique (eg, Gmail ignores dots and anything after the + sign), there's plenty of temporary email services with a variety of domains, and if you own a domain, you can trivially create unlimited emails until they catch on and ban the entire domain.

Inactive admins are also an issue, but if malicious users are determined enough, it doesn't matter that much how active an admin is. An active admin can mostly help by making IP banning an option (imperfect, but will work on many humans) and can temporarily turn on approvals to make it easier to weed out low hanging fruit. Nothing will work against someone determined enough, but could at least reduce how many instances they can turn to.

Sure. But we changed our sign-up policy recently. Users are now informed during sign-up that temporary email accounts are banned.

We have another announcement regarding this soon.

Yeah I still don't have an email associated with my reddit account. Which shocks people... although I haven't logged on in months, so maybe it's now required for legacy accounts