Byrne's just like every other creator in this respect: he may have started out with a clear idea of the limits of Superman's powers, but they were subject to change as the storyline demanded.
It's been my experience that when pros and fans (like Byrne) complain about Superman being "too powerful" what they really mean is that he doesn't get beat up enough. Byrne "solved" this by having Superman's clock cleaned on a regular basis. If fans had been clamoring for the sight of Superman with bruises, a bloody lip or torn clothes this period was paradise.
And those same people make the complaint that if Batman can't take down everyone, it is bad writing. :roll:
They have to tear Superman down both physically and emotionally because he is so bright.
They think standing for hope, fun, and life are unreallistic goals and are obscene to write about. Yuck.
The powers were not the real heart of Superman. His compassion and love for a planet that gave him a home, after his homeworld blew up, is the heart of Superman. Byrne doesn't get that.
Superman is a man of great love and great hate.
If I could ever find it, there is this excellent story where the Parasite starts draining the world of its emotional support of Superman. Superman was able to beat the Parasite after looking into a photo alblum and a picture of the Kents.
A misremembered quote:
"The people who gave me the most support are beyond his his grasp."
The new Superman might have a lot of physical strength, but he is so wishy-washy.