He was speaking the truth of the moment. They were useless at the time. That simple. And read the beginning of chapter 693, he wanted to eliminate the Biju and Naruto withheld their power.
Getting rid of Naruto because he would interfere with his plans was obvious. At the end of chapter 692 he noted that with Obito, Madara, and Kaguya gone, Naruto was the only one in his way.
Typical excuse about that scene: "He was speaking the truth".
You may call it speaking the truth, but I call it wasting time in order to be an a-hole. Why was it wasting time, you ask?
Well, Sakura asked "What's happening outside?".
Sasuke: *Proceeds to talk crap*
Kakashi: "Naruto and I want to know too"
Sasuke: *Talks more crap *
...
Sasuke: *Then proceeds to tell everyone what was happening outside, thus answering the original question and rendering his trash talk a waste of time*
Now can you honestly tell me that it wouldn't have just saved time (that could have been used for strategizing or productive discussion) if Sasuke had just skipped the trash and answered the question in the first place?
Also, was Sasuke really "stating the truth" as you a-hole fans like to say? Well, let's review, shall we?
What exactly did Sasuke do during the Kaguya fight?
Next to nothing! That's what!
The so called "useless" Kakashi and Sakura saved Sasuke's butt several times and actually did damage to Kaguya! The only reason Sasuke was even relevant was because he had the six paths yin seal! If Sakura had that seal instead, they probably could have left Sasuke in the sand dimension and still won!
Now then, having reviewed all of that, was what Sasuke said about Kakashi and Sakura being so "useless" really the truth? I don't think so.
Long story short, this would be the improved version of that scene inside the susanoo:
Sakura: What's going on Sasuke-kun?
Sasuke: The infinite tsukuyomi got casted.
End of scene
Now isn't that a lot better?