I agree with 99% of what you're saying, except that "tap-and-hold is no worse than right-click for a context menu" -- I can't disagree more, because right-clicking with a mouse cursor has both a precision that touch lacks without careful UI to indicate what I'm touching so I have visual feedback to make my touch more precise and an instantaneous response that by definition cannot be matched by a gesture which requires waiting a set amount of time. To that end, the gesture tap-and-hold works best when right-clicking in a text box as you've a "loupe" or magnifying glass that appears with a cursor to let you know where your finger is, and once you're moving the cursor, to wait and release before seeing a list of actions you can perform at that spot is relatively natural.

However, you've now made a gesture that was instantaneous with a hardware button require a LOT of UI to overcome the limitations of the smooth plane of glass input mechanism.

I'd agree that moving a mouse requires learning that when moved, a cursor appears, and you then have to learn what the buttons do, and generally that the right-click button isn't what you want. So I'm not going to say that a touch UI is easier or harder to learn, as both technically require experimentation or explanation since neither uses on-screen UI to indicate an area can be right-clicked. Users have learned to select, and to right-click, within text fields, which is why that pattern carries over well enough on iOS.

So how would I fix this on iOS? Well, I'd start by continuing to enhance drag-and-drop. Why can't I perform a gesture or click a button to reveal recent clipboard text, then drag the text where I want it? Kind of like how a recent screenshot appears on the screen briefly, it'd be nice if the same were available for text. The biggest difference -- and biggest advantage -- to the touch screen UI is how the entire screen can become whatever control you need at the cost of precision (or screen space to make up for it), while a monitor is an entirely passive experience, where the tools you interact with are literally separate from the screen and so are always available for instant use. Frankly the most interesting times will be when we've the best of both worlds -- when your laptop's lower half is replaced with touch screens that mimic mice and keyboards with haptic feedback and are meant for interaction attached to touch screen displays. That's when we'll be able to get the benefits of both worlds, old and new, as it makes sense to do so.

Another thought -- it's not that touch screens can't do instant right-click, as two-finger tap works that way today on touch-pads, but that on a touch screen two finger tap is ambiguous, you need a cursor to increase its precision. To that end, if the loupe/cursor is visible, I could imagine a power-user interface would be one which either shows the actions before you have to wait, or lets you tap after dragging in order to lock in your cursor's position and perform an action. I could even imagine that after tapping that second time, you could drag through the menu to scroll, or as Microsoft has shown countless times, use a wheel of actions centered around your finger and flick in a cardinal direction to perform an indicated action.

So I'm really not disagreeing here, that UIs are flexible, but I would say we've lost something useful with the disappearance of the mouse cursor and its replacements, just as when I switch from Mac to Windows, I really feel the disappearance of being reduced from two primary hotkeys (cmd and ctrl, with alt and shift modifiers) to one (ctrl, with alt and shift modifiers) because Windows owns its key and doesn't share it. The more restrictive your input mechanisms are (within human limits), the more creative your UI and uses of it have to be to continue to have the same amount of expressiveness as a more full-featured input mechanism would have.