That's all fun and games, as long as you realize that all browser-extensions capture your keypresses, all data on all pages, and et cetera. All browser extensions see everything you do, and everything you type, and et cetera.
Browser extensions are subject to a permissions system, just like apps. Their code is also fully visible to you, and fully sandboxed.
The only real danger to extensions right now is that they can auto-update without a user review, and thus can "turn evil". It's happened to a handful of popular extensions (eg. Stylish).
Requiring the user to manually update extensions has its own share of problems though, so I'm not even sure if I disagree with browsers makers decision to auto-update.
But the claim that "all extensions are keyloggers" is just blatant nonsense.
Ad blockers for iOS don't capture any data. They work by creating a JSON file that is processed by Safari to tell which patterns to block.