This is spot on.
I've desperately wanted to use the iPad for productivity, but even with a keyboard and a trackpad, it's just so clumsy and restrictive to use more than one app at a time that I have always kept returning to the Mac.
Like you say, the iPad lacks an identity of its own. As it stands, it's a iOS that's being stretched to make it more "productive", but the fundamental design choices continue to hamper it.
I disagree, what holds the iPad back is bad software, especially from Apple.
The iPad can replace a Mac for many people, outside of some power user edge cases.
My phone is not needing some special identity to be useful, nor does my iPad. My iPad is useful because it is the device I most like working on, even with Apples bad software quality.
Examples:
I recently discovered why I’m having such a poor pages experience and it is entirely down to Apples bad iCloud Drive implementation (the way it is trying to upload the file while I’m in the middle of editing it seems to cause some hiccups in the editing flow).
Drag and drop is harder on iPad because the same gesture does two different things depending on how long you hold for before starting. Quickly drag a finger to scroll, tap and hold some medium amount of time and the drag to drag and drop.
Apple’s insistence on hiding away useful UI behind buttons and drop downs is also another impedance, it works a little better on the Mac where you have mouse hover but on iPad where everything is a specific action it slows things down more.