Uhh, the fact is that Levitz and the LoSH crew did not know what Byrne was doing specifically. Hence why things went that way, not due to Levitz saying no. All Levitz said, as the LoSH writer, was he'd not have done what Byrne did as it crippled the LoSH at that point. LoSH was still working well.
First it's Levitz fault that he didn't make sure how Byrne's MoS would affect Legion before MoS came out Even more so considering Levitz was a VP of DC comics at the time. (Give Karen Berger some blame for this, BTW, as she was still editor of LSH back then).
And I can think of a few things that crippled the Legion worse than MoS did. But you really don't want to start that argument here, do you?