Can be done on Android without RedTube.
Is iOS on the iPhone capable of true multitasking?
Since YouTube is a video app they don't utilize the API for background playback. I believe like mentioned with YouTube red they enable this.
Your gripe should be with YouTube and how google implements it in iOS not the iPhone itself.
3rd party YouTube apps (if google didn't block them all) allow background playback on iOS. This alone should be evidence enough the iPhone is capable of it. That and the amount of music apps that utilize the appropriate APIs (pandora, Spotify, digitally imported, etc).