So in my opinion - can you use an iPad Pro for professional work? Depends on the work. If it's a single app and the task involves drawing with a Pencil... then perhaps. Anything else is just delusional. The main restrictions are screen estate, ability to multitask, copy/paste data/stencils and use of a mouse (yes, for technical drafting - you need a big screen and a mouse - fingers / pencils won't do).
This is an interesting, discussion as you and I have some commonality. I went to architecture school in the 90s and worked on build documents for a skyscraper on an early version of Autocad. Probably 90-93, or so. My exact date memory is clunky that far back. I enjoy these discussions.
I remember working on Autocad on probably small monitor. Probably a 15: 4:3 CRT. A far cry from where a "small" monitor is now a 27", and like you said, probably working in a multiple monitor setup. I was laughing the other night working on AutoCad on my iPad Pro thinking: this is nuts. almost 30 years ago I needed a beefy computer to run AutoCad; now I'm using it on my tablet. As I said before, Autodesk has a lot of improvements they need to make to AutoCad 360 before I'd consider it a "production" piece of software. The least of it is it can't create blocks and set layer color, etc. But, it's still a neat little software package. For architects, I think apps like Concepts, Trace, Procreate and the like are powerful assistants to getting work done. I was thinking if I were in architecture school again, I'd be all over this.
I don't think dong real work on an iPad is delusional at all. It's obviously situational. If you're a person who feels more comfortable in a multi monitor setup, the iPad or a laptop isn't for you. You raise good points about video conferences and working while accepting inputs on these meetings. I've never tried running something like Webex while working on my iPad. I might have to try that sometime just to see how that works.
Also, I don't really like the words "multitasking". As humans we are pretty much incapable of doing two things at once, at least things that involve output. I can listen to music and exercise at the same time because one task is an active task (working out), and the other is passive. Some people can exercise and work from a treadmill. But true multitasking: editing a Word document while editing an Excel document, you can't to. By that I mean, actively typing in Word while also modifying the Excel cells. We can't do that. What we consider "multitasking" truly isn't. I can take data from an email and copy it into Excel, but that's still one task a time. At some point and active app becomes a background app and the background app becomes an active app. The iPad has some limitations on this. Its not as easy to get data from one app to another as it is on a desktop. The process feels like there's some lag in the system.
You and I work differently though. That's ok. That's what makes human different. I prefer a single screen workflow. I don't use multiple monitors at work. I like the single-app focus on the iPad. Some of this is being a minimalist by nature. The only things on my desk right now are: a drink bottle; the MacBook Pro I'm typing this on; my iPad Pro; a pencil holder; chargers for the Mac and iPad; and a MacBook Pro I'm gong to set up for a friend to give away. I used to have two 27" monitors hooked up to two computers. I've simplified. Those monitors are under the desk.
You can make the argument I'd be more productive in a multi-monitor setup. You might be right, even. But I try to make it so I don't need multiple monitors. If I'm working with a business line for a day, I don't want to feel lost because I don't have two monitors.
There are limits to even me going full macOS at work. We use Skype for Business for IM and something in our system just isn't compatible with the Mac versions. My boss and coworkers IM me all the time. I can't run Visio natively. By "do my day" job standards, a Mac is pretty much useless.
Where I find the iPad to excel is its flexibility. It may not do all tasks I need it to, but it allows me do to a lot of tasks very well. I've outlined them before but I like just bringing a tablet to a meeting for notes, presentations and markups. If I want to hide in a breakout room and just write on a document, I'll bring the iPad me almost every time.