I’m just gonna chime in here in a devil’s advocate role. I use iPadOS as my sole (not primary, mind you, but sole as in only one) professional OS for work every day in a highly demanding executive finance environment. I do advanced and complex spreadsheets with scripting, API fetching and integration, automation, visualization and data manipulation, forecasting, dashboard creation for presentations and reports, etc.
I use a mouse and keyboard while at a desk using a 4K external monitor, and the ASK and my fingers whenever I am away from that desk, which is often.
The only reason this is possible is because of iPadOS and the accompanying desktop-by-default Safari whose user agent identifies itself as a macOS desktop browser.
Now, I use Slide Over like it is nobody’s business. All file management (Files, Documents, GDrive, PDF Expert, etc) and communications apps (Slack, iMessage, Mail.app, Skype, Facetime, etc) are always in there, as well as number crunching apps like pcalc. And the way the app picker is implemented in iPadOS makes it way more useful and simple than before, resulting in it being by far the most useful Multitasking tool on iPad. It should be brought to the Mac. Split view mostly gets used when having two websites or spreadsheets side by side.
I have become so used to the touch gestures for multitasking, and the way the mouse works in iPadOS that when I get on macOS now, I feel lost and everything feels somehow old...I clumsily get caught trying to do gestures with the mouse button held down, or move a window expecting it to slide out of view or tile perfectly to share space.
I am going to have to say that efficiency and ease of use of multitasking iPadOS is at least on par with macOS, and I am going to agree with folks here taking the view that most criticisms stem from the fact that it is not Mac-like enough, or enough like the 30+ year engrained cursor click paradigm. This is actually a strength, not a weakness, and doesn’t make it any harder to learn than a cursor based UI system. I can’t recall fumbling around trying to figure out what was interactive and what not on my iPad.
I mean in all honestly, what is so discoverable about a left click vs a right click? What intuitively tells a person, other than years and years of reinforcement, that an X button closes a window, but to actually kill a program, you need to use the application menu at the top of the screen and select quit from there, or hit CMD+Q?
I agree that iPadOS and iOS get needless tweaks and UI adjustments at times that seem to complicate rather than simply things (just take a look at Mail.app...jeez what a mess) but really, if we are being objective, what kind of interface is more of a direct extension of our human senses and natural form of interaction with the world around us - touch or pointing device + cursor?