That youtube clip isn't DX7's though, is it?!
No, it certainly isn't...back then, 1975, people still used/hired orchestras, at least in the studio.
Don't see much of it nowadays...
Sure looked pretty cool, those three synth players on stage, and it sounded even cooler to these ears; in fact, it was downright inspirational.

I've got an instrument coming tomorrow, The Tyros4, that makes the DX-7 look and sound so primitive...yet, it might not have existed without the latter's overwhelming popularity and acceptance.
Ian