Not disagreeing, but I suspect notepad.exe is the way it is for a reason - it's the Windows equivalent of vi, the thing you use to try to recover when everything else is falling to pieces. As such, it doesn't and shouldn't have dependencies on anything that isn't absolutely essential.
I believe Task Manager eschews the common control library and reimplements a lot of UI stuff itself. Same reason.
You don't really need to pull in external deps to improve notepad.exe; nearly all of the low-hanging fruit would be a few lines of code in that application itself. Even busybox's vi implementation is a more capable editor, and it's one short C file (with a handful of trivial deps on the rest of busybox for shit like the allocator and random string functions.)
I still can't believe that a hung program means the Task Manager can hang as well. I don't know how many times I've had a game freeze and had to wait on the Task Manager. Ctrl+alt+del brings up the "lock, log off, task manager" screen pretty quick, then Task Manager doesn't load until I go make and finish eating dinner.
Since that shortcut was added, that's almost always how I launch the Task Manager. Recently however, I read that Ctrl-Shift-ESC (CSE) doesn't launch the Task Manager in the same way that Ctrl-Alt-Del (CAD) will.
I went looking for the source but I only found this blog post from Raymond Chen [1]. Based on that discussion, it looks like winlogon.exe is responsible for launching the Task Manager both ways, so perhaps that more recent discussion was incorrect.
Does it still take minutes to load, though? My problem has never been the difficulty in launching Task Manager, it's been with getting task manager to respond in any amount of hurry.
I just hit CTL+SHIFT+ESC and Task Manager was there instantaneously. If things have gone so screwy that you really need Task Manager, then yeah, it will probably be slow.
I believe Task Manager eschews the common control library and reimplements a lot of UI stuff itself. Same reason.