I don't agree that these three game are or will ever be close enough to the same games to even compete with each other.
I have and like ED and NMS because they have huge galaxies, but even they, when compared, are much different games.
SC (what there is of it so far) is a much different game than those too mainly because it's not at all about a big galaxy and exploration.
SC will have a much bigger challenge completing with the AAA game scene than these other two games because that's what it's more like.
Other smaller space games like "Angles Fall First" are much more likely to compete with SC than the other two.
SC is an MMO based space combat/trading sim with exploration, FPS, resource gathering and a degree of open gameplay.
Or hopes to be at any rate.
Comparing with ED for example shows both have...or will have...pretty much the same feature list. In both, you'll pretty much be able do in one what you can do in the other. The big difference is more how the feature is implemented.
ED uses a P2P networking model for example which has its own set of pros and cons compared to the more server based system SC is planning.
While it is difficult to compate ED with SC as SC isn't released and the flight model still not finalised and debateable, ED has a more sim like feel while SC feels more arcadey.
Now, while SC plans to have perhaps 150 worlds, 100 of them perhaps available on launch if CIGs plan come together, that size won't really impact on the game too much.
The universe might feel smaller and it'll be interesting to see how CIG can keep exploration viable with such a small number of worlds but in terms of features both plan to end up with similar features.
Base building seems to be the one feature that FDev are shying away from...but even here, squadrons are getting the option for their own home base (which will inevitably leads to calls for the ability to customise it) while surface outposts for mining, etc are still being considered. So again, that would be more of a difference in how to implement the feature.
Although.....with "ten million" players, how will CIG plan on keeping exploration interesting?