Winforms is a Win32 API wrapper, so on the same level as MFC, not a separate UI framework.

It is a wrapper, but it's not quite on the same level as MFC. MFC really is a thin wrapper, almost 1:1 in most places. WinForms is more like VCL or VB6 in that it uses Win32 where it can but doesn't design around it, so in practice it's more high-level.