JimMiller is right.
UnrealEd is powerful.
Many of the functions are hidden and most of the time not self-explanatory.
The mentioned problems with vertecies and whatnot can be done with ease if you know how to use the editor properly.
Sure..there is better BSP editors out there such as RED for Red Faction. But that's another story.
I'm not sure about the "most powerful" thing, though.
I think Sandbox on CryEngine2 is the most powerful one, right in front of UnrealEd, but haven't used it long enough.
I kinda dislike UnrealEd4 on the other hand. It's too slow on every simple process.
Watching video tuts requires a lot of time, but in the end it's more than worth it.
Source has been licensed by like what.. 10 small devs? Vs. nearly 200 or something for unreal.
Now, doesn't that prove that Unreal engine IS powerful?
It is. Many of the unreal engine basing games celebrate huge success. (GoW,SplinterCell,Bioshock, KILLING FLOOR etc etc etc)