The design of Win32 is incredibly close to the design of Win16 and since Win16 dates back to early 90's you need to comparing it to GUI programming layers of that same era.
So the question is, back then was there any better GUI programming layers?
And the answer is yes, there was actually an API that was better and it was called OS/2.
At that time Microsoft was in a partnership with IBM to develop OS/2.
However, when the partnership fell apart, Microsoft just took big chunks of that OS/2 API and created a sub par version and called it the Windows API.
So the question is, back then was there any better GUI programming layers?
And the answer is yes, there was actually an API that was better and it was called OS/2.
At that time Microsoft was in a partnership with IBM to develop OS/2.
However, when the partnership fell apart, Microsoft just took big chunks of that OS/2 API and created a sub par version and called it the Windows API.