Hogwash.
Android does a truly atrocious job at using screen real estate because they screwed up and built their developer's kit around the idea of letting software decide how to scale elements. Today, YEARS later, Android still has crummy tablet apps. I have a 10" Android tablet (mid-2014). I virtually NEVER use the multi-tasking.
Microsoft allows you to multi-task, but honestly, it's rarely that big of a deal for me - I use that feature more when docked to my large monitors than when using my SP3 on its own. Microsoft has screwed up by not putting any effort into their app store, so there are effectively NO apps available, again, even years and years later. (I owned a SP1 as well and thought the situation would be better today. It's not.) The one thing Windows does well is allow for quick scrolling through open full-screen apps with edge gestures, but iOS does this as well. They both work great and I find it far preferable to having multiple apps open side-by-side the majority of the time.
Further, allowing side-by-side apps, which Apple will likely offer soon, speaks to nothing of the quality of the apps themselves, and how well they use the available space. In that category, nothing touches Apple because they designed the system correctly from the bottom up, and have by far the largest pool of top developers creating apps for their devices.