Me too, and I am a native English speaker from south east England. I certainly say 'it is so.' Maybe it is age related, as my generation grew up with a much more formal spoken English than is often used nowadays!
I tried just for interest's sake, ʾfor the time beingʾ for per il momento, which was not accepted, if course, but probably what i would have said.
They don't seem to have worked out many alternates here.
I dont' understand why so many posts have to do with how the sentence would/could be spoken in English and what should be marked correct in english. When we are trying to learn how to think in Italian, so ... è così is one way an italian speaker would phrase this idea.