I dunno, looking at it there it still makes my eyes happy. Also very easy to understand whether you're 4 or 84. Didn't Apple once pride itself on accessibility?
The only reason you see it as 'dated' is because it never improved because iOS 7 happened. If it kept being developed we might have even more amazing features on the Vision Pro or possibly holographic UX ala the Iron Man movie. You're seeing it from the year 2012 where it stopped.
But when I see flat design I see washed out, boring, bland, white, blinding, migraine inducing, reminder of the DeskMate and PC/XT era. It's like comparing a 'modern' home interior to one from the 1970s. I prefer the '70s one, with warm lighting, nature-inspired colours, soft carpeting, while the 'modern' one is like living in an office cubicle, all white, no colour, 5000K LED lighting, no decor, and worse, those wall-art pieces with 'Live Laugh Love' all over them in that horrid swoopy font that makes Comic Sans look good.
I don't know, when I get home I don't want to feel like I'm still at work, and when I use my iPhone or Mac, I don't want to feel like I'm back in the '80s or wanting to close the LCD lid or put the phone away as fast as possible due to the UI making me dread looking at it. I guess getting your things done on your phone and putting it away fast works for efficiency but back in the iOS 6 days I enjoyed my phone now I just hate it.