I’d say it depends on the size of your library and your expectations on library management.
The SC5000s work well as standalone players. My gripe is with library management.
First, you still the laptop to compose your library, organise your tracks in crates and analyse them. You do that with Engine software, which at the moment I find excruciating to use.
Once you have your library ready, you can use it standalone in your SC5000s (and Prime4) without further assistance of a computer… with one caveat: big libraries (more than 20k tracks) are very slow and search to navigate in the SC5000s (it takes like 8 seconds to search or change crates, albums etc). Furthermore, you can’t search by comment.
So, if you are the kind of DJ focused on one genre and with a library less than 20k tracks, yes, it’s totally usable standalone once you have done the preparation in Engine.
If you are the kind of DJ with a huge library, taking random requests from people, and relying on search, it may not work for you.
I’m the second, and Traktor, Serato or Rekordbox pro-link work for me in that model, but not the SC5000s because of the issues mentioned.
Also, the FXs of the X1800 (and I guess P4 will be the same) are in my opinion worse than the ones in Traktor or Serato. I miss a good delay or echo with a long tail.