My criticism of MacOS Spaces is one I have of all Apple's window management efforts over the years: It's a great start and a foundation to build upon, but they never really followed through with iterative improvements informed by real-world usage.

In Spaces' case, the problem is a combination of an overly rigid model (only two full-height windows per space) and high friction to management (the process of moving full-height windows from one space to another requires multiple steps). Traditional free-form windows are a little better, but it's easy to lose track of them because the overview itself requires two steps to access (open Mission Control, hover the top bar to expand thumbnails). These could have been gradually improved over the past 14 years, but Apple has somewhat frustratingly left these core workspace features to wither on the vine.