Oh, I wouldn't consider Metro style apps as any kind of replacement for desktop apps or most professional tools. I've been running Windows 8 for a while now, but to me on desktops or larger screened laptops they are just fancy gadgets that live off the left side of my screen. I like having them because they are isolated and suspended when not running, so I can use lots of them without impacting the system (or even cluttering the taskbar). I just grab one from the switcher or the start screen, check something or do something simple, and then click in the upper left corner to go back to the desktop. It's a bit like I might have a phone next to me while using a PC and check mail on it sometimes, but there are some advantages such as being able to use your keyboard to enter text, being able to click on a link and have it open in the desktop, etc. However for integrating into any more involved workflow I would stick to desktop apps for the reasons you mentioned. (I also agree that the Metro open file dialog is really lame, it somehow manages to be even worse than the Windows folder browser dialog and I didn't think such a thing was even possible).
There is a lot of weird FUD about the desktop being "legacy" and on its way out, and although that's not something Microsoft has actually said it does come partly from them being overeager to hype their new thing because it's their new thing, and partly from the press echo chamber liking to hype things in general. But it's completely absurd.
re debugging, I think there is an "emulator" you can use which is really a remoting session into your own machine, but it will run your app in a window.