I love how people try to make the OP feel like their wants aren't valid with the lame "then get an Android" response. Plenty of people want Split Screen on an iPhone, that doesn't mean they want to make the change over to Android. It means they would like that feature on the best phone on the market. "It makes the usable space smaller" isn't even a valid argument. We all lived perfectly happy lives doing our daily routine on a 3.5 inch, 480x320 screen when the 3GS was the phone everyone had to have. I'd LOVE to be able to continue watching a video and check my twitter feed, messages, or even use it for copy/paste between 2 different windows ON AN IPHONE...not some crappy Note9 filled with bloatware that can't even get the latest updates until months after they're released. Even if that means the usable space is temporarily smaller. People who continuously post "We want dark mode" aren't met with a bunch of people telling them "then get an Android" (though i do see it sometimes, lol).
I get your point, but I think people revert to “get an android” because that’s the only option. We can all sit here and complain to the internet about wanting this feature or that feature, but it ultimately makes no difference. If you prefer iOS, the features will come eventually. If you need to have every feature that’s out there, maybe Android is best. As I mentioned above, it was likely planned for iOS 12 and the 6.5 inch phones, but they pushed it back to focus on performance. Something that benefits everyone.