I can't think of any email clients that automatically download external images by default. The article seems to be over-blowing the issue a bit.
GMail displays them. It uses a proxy for downloading, but I don't think that matters unless they're preloading all images unconditionally upon server-side receipt of the message.
Apple's macOS Mail.app client displays external images by default, as does their iOS app.
Privacy defaults come down to usability vs. privacy; Apple making this so easy to toggle is fine by me as I care about privacy and tracking.
Now, it would be great if every macOS application walked you through privacy settings right after installation in the same way that I am offered a tour of the new features. Since there is no such "privacy tour", the community has discussed ways in which macOS can be hardened [1], [2].
1. https://github.com/drduh/macOS-Security-and-Privacy-Guide