The iCloud enabled MacBook is the one leaking memory. I'm leaning towards a hardware issue because the iCloud setup is the OS default and the number of reported issues is still low.

Edit: A recent reddit thread may have correctly identified the WindowServer leak being related to the amount of full screen video played. My impacted MacBook is often used for Netflix/Hulu content. https://www.reddit.com/r/apple/comments/qos5n5/memory_leaks_...