A "normal monitor" often comes with a PC built in.
People who claim that a tablet or a smartphone will kill PC are on some heavy drugs. Or they don't use their PC, which is another good possibility. Most home users do not need anything beyond web browsing and an occasional email. For them a tablet or a smartphone is more convenient if all they need is a Facebook appliance.
Businesses and the industry, however, operate on slightly different principles. There is even an ancient term for that, "work." Tablets are useless for most of that. Exceptions include mobile workers in warehouses, hospitals and such. Everyone else wants to have a large screen in front of him - the larger the better. Have you ever seen Jean-Luc Picard taking a video call from Starfleet on any of those little tablets that engineers were running with? I'm sure those tablets were capable enough; but it's just inconvenient to look down at the tablet as you speak to your boss. Privacy and secrecy also matter. For that reason Picard had a desktop in his ready room, and that desktop had a nice large screen.
Multitasking is essential for work because nobody can produce a 100-page document without referring to other materials. That's why you need to have many windows that you can see at the same time.
PCs in business represent the majority of PCs out there. They will be changing, but the direction of that change is not toward tablets. They will be increasing their performance at the expense of power consumption; they will be increasing display surfaces (a dual monitor setup is common in many companies already.)
Tablets and smartphones are severely constrained - by power, by size, by cost. Manufacturers are doing their best, but it is not possible, logically or otherwise, to merge an office supercomputer and a pocket gizmo. And why would you want to do that? If all you need to access is the shared data, then why don't you share that data over any network or storage method that we know of? There is no reason why your smartphone should contain drawings in E format - you can't see them on that tiny screen anyway.
That’s why I then suggested being able to easily slave the tablet to a normal PC, with syncing being real time and instant. The stuff that the tablet can carry around may be limited (as you said, complex graphics would be useless on the tablet) but you would want that stuff both when using the PC and when using the tablet alone.
And anyhow... maybe you’d want to pull a complex graphics file onto the tablet in spite of not being able to view or edit it on the tablet, so you could then pull it off onto another PC elsewhere.