To answer concisely:
does Unity and UE4's audio engines stand up against FMOD and Wwise?
it's good enough for most people who are doing audio in their games where interactivity with the audio is not a primary pillar
Do they have all of the parameters, interactive capabilities, and functions that the middleware do?
not all of them, but the general gist is that since middleware is taking the parameters that drive interactive audio from the game anyway, you should theoretically be able to recreate most - if not all - interactive capabilities in code, one way or another.
Is it worth using FMOD if the engine covers all of it?
It's always helpful to keep in mind as well that this is very, very much a matter of preference! In your question you used the word obsolete, and I think that "obsolete" here is a very strong word - it'd be difficult to call middleware obsolete just because Unity has a mixing table now. Wwise and FMOD can be used for free in many projects with smaller budgets, and larger budgets would have the money to deliberate whether or not they want to use Wwise or FMOD in whatever engine they choose. Many game engines lack even the more basic audio functionalities that many of us take for granted. The world is a far bigger place than just Unity and Unreal and it's a heck of a lot easier to hook in Wwise or FMOD than it is to mix your audio in code or hard mix the .wav files. As an aside, the world is also much bigger than even just Wwise and FMOD as far as middlewares are concerned...Fabric is getting pretty popular and many proprietary middlewares like Scream are popping up now and again too.
The reality is that there's choices and it's just about helping your audio team create the vision for their game. Use what works, and don't worry about the rest. ;)