Henshaw destroying Coast City could make a movie in itself. But he's better off being set up in the Superman franchise first before moving to GL.
Since that isn't an option at the moment he's not useful enough to keep around in a SWC adaption.
What works in comics doesn't always work in movies. This is not an example which can do that. That screen time would be better used for events which move the story forward.
DC doesn't have to copy everything Marvel does to succeed.
All it does need to do is make great comic adaptions.
They can do that with franchises in their own continuity where characters meet each other like JLA, Outsiders, Teen Titans, World's Finest, Brave and the Bold, Suicide Squad, Super Max etc.
Green Lantern's mythos has so much potential they could do several films without interacting directly with the DCU at all.
They'll keep what works and scrap the rest.
I know its hard not to have every detail in adaptions of your favorite comics but it's unfortunately something movies can't avoid most of the time.