That doesn't make them bad -- just hard to discover.
Once you find out about them, they are dead easy.
Not all UIs have to be immediately apparent, UI design is also about teaching users new idioms. Pointing with a mouse was alien once too...
Another example, a great feature in Google Maps on mobile is the ability to zoom with one hand. You double tap and drag (tap, tap-and-hold, drag), but I only figured this out because some blog talked about it. From what I can tell there are no instructions in the app that tell you about this feature, and I see this as being in the same vein as 3D touch. Sure it's great, but if people don't know about it or can't learn about it easily, they won't reap the benefits.
It's fine for secondary controls (other ways to zoom). I'd say Google learned the lesson with the now discontinued Menu button on Android. Application authors would sometimes hide critical functionality behind a Menu button press, and sometimes the Menu button did nothing. This lack of discoveribility and inconsistency is bad for User Interaction
This is a native Android gesture, by the way, and works in most apps and web-pages. It used to work on HN, but stopped when they changed the markup to be more mobile-friendly.
Someone shows you, you see someone do it, you accidentally press and activate it, you watch the introductory "wizard", you see it in an iPhone ad -- there are literally tons of ways.
Including the one everybody hates, RTFM...
What I mean by that is that OS X has hundreds of small features, keystrokes and affordances that are probably documented somewhere, but that I and most other people tend to find either by accident or by being told about them.
Apple's products have always been this way, and I rather like it. It is similar to my learning experiences with physical tools - over time, I've found a lot of tricks and 'off-label' uses for various woodworking tools by experience, and the OS sort of mimics that process.
For whatever reason, it doesn't work as well on the phone. I suspect it is partly that I don't spend hours at end doing things with my phone - I look something up, send a text, call someone, whatever and put it back in my pocket. A second factor is I almost never do complicated things on a phone. I have edited code in vi and then pushed/deployed it from my 6s, but not by choice, and that's not even that complicated.
So I do think discoverability is somewhat worse on a phone, at least for the way I use one, and it seems like an indirect form-factor consequence. It isn't that the form factor can't be used for complex tasks, but it is much more comfortable elsewhere, so the phone stays relegated to simpler stuff, which doesn't lead to the same degree of discovery/experimentation/happy accidents.
You can quickly switch apps using 3D Touch? How?