I would say the only real "disadvantage" Wavelab currently has is lack of built-in DDP support. It's available as a very expensive add on. I think what makes the difference in price between Wavelab and say, Pyramix or Sequoia is that the latter two can do EVERYTHING from tracking all the way to mastering very well, with flexible routing mixing and monitoring whereas Wavelab is excellent for editing batch processing, mastering and creating discs and that's it.
So when it comes to final editing and mastering duties, I can't think of anything I'm aware of another Mastering DAW doing that Wavelab can't. And everything in Wavelab is incredibly easy to do. I think the most important thing that causes one person to choose software A over B is how easy it is to get around and work inside the program. Sequencing and coding a CD in Wavelab is very simple, in the Samplitude demo I have it seems weird and illogical to me, just my personal preferences.
For example, I love Wavelab but I really hate having to set the cursor and then press "S" in the montage to make a cut. The other option is to double click in a specific "zone" to cut. I really wish there was just a scissor tool(like every other DAW on the planet) that I could select and make a dozen cuts as fast as I want. I've asked WL's programmer Philipe about it and he thinks the idea of a dedicated cut tool is ridiculous. Also, WL sometimes won't read all of the CD text I inlcude on a disc USING WAVELAB but plextools reads it all just fine so i can be sure it's there. Little, irritating things that go away with each update.
All the functions are there, they just have different names and different implementations. WL has clip effects, Sequoia calls it object effects, etc. I guess you just have to demo everything and go with what you like, but I wouldn't feel guilty about using wavelab because it costs less than other programs. It's just taken WL a while to get to where it is today and in that time there have been other programs to suit the needs of ME's better, but I don't think that is the case any more.
So do I love WL 6? Yes. Am I looking into Sequoia and Pyramix? Yes. Have I yet been able to justify the cost vs what WL 6 is already doing for me? Not by a long shot. The metering, delay compensated everything inlcuding external effects loop, the smart bypass (WL exclusive I believe)and ease of use keep me a loyal WL user.