Hi there!
I have both Cubase 7.5 and Wavlab 8 and Wavelab has way more edit functionality then the included Cubase wave editor.
Still the included audio editor in Cubase are very powerful. I would say one of the most powerful edit capabilitys on all professional DAWs.
Wavlab give you further audio editing , audio analyzing and audiofiles managment. Its also an audio editor in full native x64 so it will work with all your installed x64 plugins. Like so many else I only have the x64versions of all my plugins install on my computer. No 32bit.
So example Soundforge that are still only in x32 can only use x32 plugins. Also if you compare Soundforge with Wavlab, Wavelab Elements 8 have even more functionality then the latest fullversion of Soundforge.
So no brainer if you need a great audio-editor. Wavelab are the best on all counts!
Best regards
Freddie