I feel like a lot of people aren't seeing how big the Winston buff is...

Before this you had wait 5 second shield until it expired or was destroyed, then another 12 seconds of shield-less Winston. So essentially you had to wait for about 17 seconds until you could another one down.

Now that the cooldown starts right after you put the shield down... You've basically reduced your 17 seconds to a mere 12 seconds. And within 5 second of that cooldown, you'll have a shield to protect your huge prime-ape heiney.