They might have stated things in a way that was embellishing, but boy are we FAR from the "Yes there is multiplayer and yes you will be able to see other players in the game" no man's lies.

They never said you'll be able to "Witness large random ship battles out at sea" or even "Take part in them, chosing a side to fight with". (But in SoT you actually can witness ship battles out at sea and pick a side (Usually yourself)).



They never phrased it like "When you get to 50/50/50 and become a legendary pirate, a surprise awaits you" and give you the middle finger of making you start over from scratch. They did say what you'll do when getting there: More of the same.

And we accept that when buying the game.

 For SoT they merely tried to embellish things but I don't think you can compare both in terms of lying.

On the other end, on the question of endgame: Yes, repetitivity is a problem. Yes you might be able to compare No Man's Sky and SoT in terms of repeating the same things with little rewards and little meaning. The biggest difference I find here is, again, the multiplayer experience. Most people here will tell you SoT is the funniest multiplayer game they played in years, and I agree. You truly have a wonderful feeling while manning even a 2 man sloop and battling through the seas, even if it's for a f-ing castaway.  
In the meantime in no man's sky you 'enjoy' alone some colors, weird looking weird sounding animals while lasering away your resource to get to the next planet. Again and again. No challenge, no friends, no fun.