Apple deletes some of the false positives outright. They never even appear in the Junk mailbox. This has been going on for many years. It’s also no longer possible to turn off Apple’s server-side filtering, e.g. if you prefer to use another filter such as SpamSieve. These days it’s easy and inexpensive to host e-mail on your own domain, and there are free e-mail services that are better than Apple’s, so I see little reason to use iCloud for e-mail.
I’ve been telling friends and family for years to think twice before using a Gmail or iCloud email address — or even worse, the email address provided by one’s ISP. The problem is lock-in — once the world knows you @gmail.com or @earthlink.net, it’s not easy to change when you become concerned about Gmail account hacking, or when your ISP goes belly up.
Regarding spam, since setting up my own [home-based filtering system](/2012/08/11/running-your-own-server-side-spam-filter-with-spamsieve/), I’ve had absolutely no need for the types of server-side filtering services offered by Gmail and iCloud.
(And for a bit of added security, I have the incoming messages on my publicly-visible email addresses redirected into an email account on a domain that nobody knows about. So if anybody ever hacked into one of my known email accounts, they wouldn’t find anything there.)