This is really no different than OS X, except that it somehow is different.
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.