This from The Verge review of the 2015 rMBP...
"there are still occasions where the MacBook Pro is simply overwhelmed by the amount of information it has to animate on the screen. This most commonly happens when switching in and out of the Mission Control multitasking overview with a bunch of apps open. I may be willing to forgive such infractions on my MacBook Air, which trades away a sliver of performance for better battery life and a thinner profile, but the Pro is supposed to be the no-compromise MacBook."
I rest my case.