Living in the future is better than living in the past. Accept the future!
Except that your future seems to be very different from mine. I'm not a programmer, I'm a full time graphic designer. Being able to see a huge Excel list, multiple InDesign files, a Photoshop window and a browser at the same time, spread across three 27" monitors, is crucial to my workflow. I cannot switch between Excel and InDesign, for example, since everything I change in one of the windows more or less directly affects the other.
Or even leaving the multi screen debate, what about InDesign itself? Placing an object pixel perfect on cut path I got from the printing company is not something I can do by dragging it there – I have to enter coordinates, which is much faster when I have a keyboard. Or when I need to quickly open a Photoshop file, change multiple smart objects which are stored across different file servers, and then automatically refresh the .psd in every InDesign document I've placed it?
What when I need to work on a project in Cinema 4D? My Mac quickly connects to our render farm, giving me hundreds of teraflops of processing power whenever I need it. I don't know of any iPad app that can do that, and I'm not even sure if Apple would allow such an app in the App Store.
A touch screen is - due to the nature of your finger - also far less precise than a mouse or a trackpad. Sure, you can use the Apple pencil, but switching between the pencil and the keyboard all the time grows tiring far more quickly than using a mouse and a keyboard, especially when you work ten hours non-stop, five days a week.
Heck, the 12.9" display doesn't even allow me to view an A4 spread at full size. The iPad doesn't allow me to use external GPUs, or to use the power of huge tower PCs to support my workload. It doesn't even allow me to natively access files on a local file server, which is crucial to a workflow in an agency with dozens of graphic designers. The files app, while it's a nice thing, can't replace a file system for more complex workflows.
Let alone the advantages of Scripting. Apple Script has saved me so much time, I wouldn't want to give up that option. App availability is a thing too. Need to use Capture One? Premiere Pro? After Effects? InDesign? Illustrator? Well, your iPad is out of luck.
When switching from an iMac Pro to an iPad Pro, you give up so much, and get so little. The iPad is a great accessory to the Mac, when you want to scribble something on the go, or when you want a cheap graphic tablet to use with your Mac. It's absolutely not a replacement for one. Not now, and if Apple doesn't significantly change iOS, it never will be one for full time graphic designers. I can absolutely see how it could replace a computer for many other people though.