In a home game, it’s possible for the GM working with his/her players, to adjust the tone of a campaign (even a prewritten one) from grim to noble, dark to bright, serious to comic. I’ve played comedic noblebright games of Call of Cthulhu, serious grimdark games of Bigs Eyes, Small Mouth, and everything in between. However, in an organized play environment, a GM doesn’t have this same degree of flexibility. The general tone of the campaign needs to hew closely to the same standard from table to table. Sure, specific modules can be tweaked and individual GM style will vary, but you’ve only got so much leeway.
I’d say that Shadowrun sort of defaults to mostly serious (but with satirical elements) Grimdark in most of the SR4 and SR5 materials. That’s the “cybernoir” style OP mentioned. But the older editions of SR1 and SR2 were a lot more Grimbright, since it felt like the ‘runners could make small-but-lasting positive changes in the setting. That was the more “cyberpunk” feel. SR3 strikes me, in hindsight, as a transitional phase betwee these two styles — the Renraku Arcology Shutdown being a key moment when things went from Grimbright to Grimdark.
In a Grimbright version of that plotline, you’d have basically the exact same story and the exact same sequence of events. But the aftermath would have been different. In the official canon, the post-shutdown arcology is now low-income housing. There's no funny plothole, because that means millions of people are stuck there without any hope of advancement, being given the cheapest possible food, water, and clothing, shown only corporate propaganda, with their only chances for money being the most menial of labor. And they can't leave. Ever. After all, this is supposed to be a self-sustaining facility, right? That’s some serious Grimdark right there!
A Grimbright ending would have seen it turned into low income housing, the millions of people being warehoused in it doing menial labor... But there kids are all getting top-notch education and have a real shot at good jobs when they’re an adult.
Older Shadowrun often had an ending like the “good end” of a Fallout video game: sure, it’s still a post-apocalyptic landscape, but because of some actions you took during the course of the game, things are looking up. Roll the credits over a field of green grass and a few freshly blooming wildflowers.
Modern Shadowrun often has an end long like a Neo-Noir film: everything ends up worse than when it started or (if the characters are very lucky) just goes back to status quo ante: “Forget it, Jake: It’s Chinatown.”
Neo-Tokyo’s not the darkest or the grimmest part the Sixth World, but it’s a lot more Grimdark than Seattle or Chicago.
