...A load of stuff I don't think about things I didn't say.
I couldn't care less about photoshop. Graphics is the only thing iPad and pencil CAN start to do. Professional design software isn't available on iOS, and it isn't coming. Some of these design applications were built in the 1960s in the space program and have decades of development time in them. They modify and utilize the OS in enormously involved ways to be as capable and powerful as they are, and sell for many thousands of dollars per seat. We can't even get the most popular, mid-level design software companies to consider writing for OS X yet, much less iOS. If you expect everyone to suddenly just start rewriting new versions of their software from scratch to fit an OS that can't even link a spreadsheet or database to a drawing, for use on a single manufacturers consumer-level device just because it's neat, you're going to be sitting around waiting, not working, a very long time.
iPad & pencil are great if you want to take some notes and doodle some sketches. Those are the 2 things it does. For the other million or so things, we can use Apple because OS X can run in conjunction with a secondary OS, and a fully capable Wacom Cintiq with customizable context menus optimized for the software and workflow. That's what professional means. OS X on a tablet would be that. An OS optimized for a phone isn't.
That's not stuck in 2001, that's stuck in today, and in stuck in at least the foreseeable future.
If you're talking about CAD, then there definitely is professional design software in the works. The reason CAD on tablets hasn't taken off like all the futuristic tech videos promised it would is because it needs precision, and using your fingers to manipulate these fine details on a 2D plane is tricky. Your fingers weren't designed for that. For that level of fine control, you really need to use a tool like a stylus or mouse (where you have several fingers and your hand giving stability and precision).
The iPad couldn't always do "graphics". It could do painting and inking, but the finer kinds of line art are only possible with a more precise tool. It's the same interface problem as they've had for CAD, and that's something Apple is addressing now with the Apple Pencil.
You seem to be expecting impossible things of the tablet market, though. We are still only a few years in to this market, and for all your non-specific ranting about iOS, it's currently the only tablet platform to be seeing any kind of success in the marketplace. Like you said, this legacy software took decades to get to where it is on the desktop, and you're going to need to be patient before applications on tablets reach that same level. These big legacy products will probably be some of the last holdouts; they need massive demand from customers before they do that, and it's simply too early for that much demand to exist.
Linking a spreadsheet to a drawing is totally possible on iOS. Again, you're stuck in the past - you're thinking about sandboxing on iOS. Sandboxing was actually an incredibly wise decision by Apple; they decided to make the platform secure from Day 1 and stood by that under a lot of heat. With iOS8, though, they added secure inter-app communication to solve some of the limitations of sandboxed apps - You can now open files stored inside other apps, for example (without copying - the other app's sandbox is given authorisation to use that one file). That was a big request, especially for productivity software. Even then, lots of professional software is just fine keeping all of its project files together and in-app. Better, even.
Legacy Software which modifies the OS is not going to fly in today's world, full stop. Even on the desktop, both OSX and Windows have been clamping down on access to system files in an effort to make real progress on security. Those legacy packages are going to need to be updated to reflect the changing systems we use - that means they'll need to work on more secure systems where system modification is restricted, and if we go that route, to touch/stylus-based interfaces too. That's true for all software.
The stuff you're saying about iOS being too small for businesses to care about is totally ridiculous. Probably the biggest productivity suite in the world, Microsoft Office, was released on iOS long before touch-optimised variants came out for Microsoft's own platform! That "single manufacturers consumer-level device" is far-and-away the best tablet on the market right now; it's as powerful as an Intel Macbook from a couple years ago and improving massively every year, has incredible battery life, weight, screen, and isn't expensive. As far as legacy software goes, it also has outstanding compatibility due to its common core with OSX; essentially the only differences between iOS and OSX these days are at the cosmetic/UI level.
