I agree with Argo about the change in writers, which was why I'm excited they brought in Jay Faerber.
Oliver, Barry, and Kara are the TV trinity and I can see them and Superman taking the leadership role during the Crisis.
I dont see the need for Superman, anymore than I saw the need in the last crossover. You have a Super.....use her this time around.
Normally, I'd agree with you, because I love the emphasis on Supergirl. But Superman and Supergirl are both absolutely crucial to this story, even in the comics. I think Superman needs to be involved. That's not to say they should backburner Supergirl for it. But it's a multiverse ending threat. He needs to be there. As a fan of the source material this story is based on, Superman NEEDS to be there, alongside Supergirl and The Flash.
Crisis on Infinite Earths will only be made into a live action story ONCE. In our lifetime, at least. As such, I want him included because I want it to be as faithful as can be.