Where’s the right button or indicator of opt+click
It’s not a failure of UI, it’s a failure of utilization. Had there been better uses of 3D Touch it would have been fine.
Also the fact they needed to support interactivity without for other phones they could never really use it for anything ground breaking. Same issue we have with not being able to fully take advantage of larger screens because you have to support the small ones too.
Everything doesn’t need big blatant arrows pointing to it to let you know about it.
For the mouse you have there, it's a bit different—at this point, right clicking is already a decades-old established paradigm. They're taking your knowledge of how a mouse works and telling you, "look, this doesn't look the same, but it works the same. Just pretend like there's a button there, and we'll take care of it for you."
Option-clicking was similar, at some point—because the Mac started with only one mouse button, using keyboard modifier keys was a familiar paradigm. I would bet that about 75% of the time you talk to someone that's well acquainted with option-click started with an OS before OS X. (That's a guess, obviously, but honestly, option-click is not something I feel is well understood by Mac users anymore.)
I'm not saying that everything needs arrows pointing to it, but there are some elements that are *obvious* when you sit down at a Mac with a keyboard and a mouse. You can type. You can click. There's a menu bar.
Some of iOS' best functionality is incredibly cryptic, and you can tell that it is because every friggin' week there's another stupid article with a title like "7 things you didn't know your iPhone could do". And I read all of them and every once in a great while, they're RIGHT, even though I read the release notes for the OS and watch the WWDC keynote and install the iOS beta as soon as it's available, etc.
I'm not someone calling for a return to skeuomorphism or trying to cram a desktop interface onto the phone, but how the hell are you supposed to know that swiping down from the right corner does a different thing from swiping down in the middle of an iPhone X(R/S)? There's no indication that swiping down is even a thing anywhere on the screen. It's not great interface design.
I believe in the general philosophy of iOS as a system (get out of the way, let the apps do the work), but telegraphing some functionality would only help the OS.