Vlad I see that support for iCloud E2EE is planned, so I look forward to giving Orion another try when that's ready. I understand why it wouldn't be your top priority.
That said, E2EE is a privacy matter by any technical definition I've ever seen working in information security. Data mining for ad targeting is also a privacy matter, but it isn't the only risk E2EE protects against. Even then, I'd be more concerned about Apple's rapidly growing ad-tech division than Mozilla's actual business model of providing Google antitrust insurance. Also, you've argued that people should trust Orion because they can break out mitmproxy and see for themselves what it's doing; the same goes for Firefox Sync and Apple's operating systems, but not how Apple handles iCloud data.
Again, I'm not trying to change your mind about priorities, just trying to leave the discussion of privacy in a better place.