It's easy to say a Kyle-led title could have done just as well under the pen of Geoff Johns. But Rebirth was about more than the return of Hal. That was a key unifying element, and provided the sense of a fresh start required with the continuity quagmire the Green Lantern title had dug itself into. But it wasn't just the return of Hal. It was the return of Sinestro, of Coast City, of the Green Lantern Corps, of so much of the mythos that had made Green Lantern a great concept in the first place, that had all been abruptly wiped out in order to give Kyle Rayner a niche.
I agree that has something to with Hal's success but they could still bring back those characters with Kyle as the lead or in his own high profile series.
Still, what happened in Rebirth would have been a temporary spike in popularity among the non-Hal/classic GL fans had Johns moved onto something else and let a less profile creative teams execute the new volume. Johns' has been the main reason for GL's success, not Hal or the mythos.
While Sinestro, Coast City, the GLC are good concepts they could have been bought back with Kyle. They just need good high profile writer and artists do them justice. Hal's been much more lucky then Kyle in that respect. Without it they wouldn't be as popular as they are today without Johns or his incredible army of artists.
And when you consider that Hal was turned into a villain, wiped out much of his supporting cast and the stuff that made his mythos special to fans, before ultimately dying himself, I'd say that Kyle fans got off relatively lightly.
Kyle was turned evil and given much worse treatment as Parallax then Hal did. It may not have been as long but he wasn't given as much the same respect in the role. He was either a victim or a two dimensional villain.
Just because Kyle fans wre treated lightly doesn't eman they have to shunt Kyle off to a lesser role in the DCU. He does have a loyal fanbase and can reach the same potential Hal can IMO. He's just never been given the opportunity.
By comparison, being relegated to a prominent role in GL's secondary title (which is also great in its own right) isn't such a bad fate for Kyle.
Which still isn't equality.
GLC isn't just a secondary title, either. As good as the title is its still a massive downgrade for a character which kept the franchise alive for 10 years. He deserved more then that. Im sure the Hal fan base would feel the same way had the roles been reversed with Kyle keeping the flagship and Hal being only in GLC.
He should have got something like a series with Morrison and Quietly.