Actually, except for the window expanding to full screen, overlapping the taskbar and so on, I have occasionally seen Windows Explorer exhibiting this "locked up, won't respond" condition since upgrading to Windows 10. Internet Explorer as well. Typically when I am searching for something using Windows Explorer, where even the progress bar for the search locks up, and trying to close Explorer just won't work. Although I have never seen the popup asking if you should wait or close the application. I also see long delays to display the contents of a network folder using Windows Explorer, and at other times it is almost instant. I do see the issue on MC at times. I nearly always just tell it to wait, unless I don't have time. It often comes back within seconds, and sometimes never comes back, but usually only if I have been doing a lot of tagging or moving of files, or using a Client extensively and them return to use the Server.
So I think most of the issue is an OS issue, but I have been unable to determine what is driving that it. It could be my virus scanner trying to check a whole disk, it could be the Windows Indexing function trying to index and/or catch up on the file changes. Sometimes Windows even tells me it is indexing files. It does happen too often in MC, but then for me, MC is often making small modifications to many, many files, and so either the virus scanner or indexing could be the issue. It does look to me that MC is waiting for some other thread to complete, or even more likely, MC is being prevented from doing anything until some OS thread has passed control back to it. It could be that MC retains a lock on the last file it touched (or seems to always) and some other Windows process (virus scanner or indexing) is waiting for MC to release that lock so it can do its thing and return control to MC.
The comparison to SAP is entirely unfair. MC looks like it has a database, but it is actually a flat file system that is programmatically operating as a database. SAP running on Oracle or any of the other options runs a full-blown database server with built-in database functions. Much of the data processing is happening on highly optimised algorithms built into the database. Often the User Interface is a thin Client and is not doing any processing, so it can go on and do other tasks, particularly handle user interaction. CAD\CAE programs operate in a very similar way, unless you are running them fully on a stand-alone Workstation, and even then there are support services running under the hood. Not a relevant comparison to a US$50 consumer product at all.
But I agree that I see it too often with MC, and it would be nice to know why, and how to avoid it. However I think it might be installation specific, with Windows, Drivers, other applications, and Hardware all contributing. So very difficult to find a definitive answer.
Regarding the window expanding to full screen, overlapping the taskbar and so on, I think you need to look to your video card, driver, default Windows resolution, and so on to find an answer. There are a few, very few, situations where Windows will sort of defocus the current window and change the resolution, font, or something. I can't even think of an example at the moment. Nor have I seen it in a long time.