Prior to MacOS 10.11, Mission Control was good: you would swipe up with four fingers and it would show you a preview of all of your spaces. Then in 10.11, for no discernable reason, they changed it to suck: rather than showing you a preview, the bar just says "Desktop 1", "Desktop 2", etc until you mouse over it; the practical effect is that using spaces is disorienting and requires memorization.

Some third-party software pretends to restore this functionality, but they do it by repositioning the mouse to simulate a hover, which introduces a delay and doesn't integrate correctly with the animation. Someone wrote a patch that works by disabling SIP and injecting code (https://github.com/briankendall/forceFullDesktopBar), but eventually stopped maintaining it.

A decade later, I doubt anyone at Apple remembers that this bit of user interface used to be good.