This is a really good reply! I wasn't expecting this.
I'm not sure I believe you that late game teamfights are over as quickly as you state - Sure, many of them CAN BE decided by a single rotation of abilities... but its not always the case, and I believe I could find high level play evidence to suggest such. I think there are a lot of genuinely good 'lengthy' teamfights that have good interaction, good strategic depth, and are really fun to watch. That being said, I also concede that there are many points in the late game where certain champions become unstoppable, or that certain champions just enter 'burst' mode where they can explode someone in a few seconds. I believe this is by design, and I think its overall healthy for the game. I don't really want to see late-game or mid-game scalings pulled back. (well, maybe a bit! but like..5-10% tops!! ) It feels like your complaining directly about damage creep here, which they are addressing. If your complaining about late game damage output, I think we'll probably never agree, and I don't think your problem is solvable.
Some fights are decided too quickly, and I don't think a global damage nerf is the answer, to put it bluntly. I agree with you there is a problem, but its so much more complex than what your saying. I think it's being addressed.
Furthermore, I think 'twitch or reflex' style playing is critical to leagues success - I think that you need both to be successful at the game. When you slow the pacing of the game down, It gets a bit more boring. I tend to favor the 'quick-paced' nature of the game that keeps it feeling more like an action game and less like a strategy game. That's just my opinion though - and I do agree that we could use some minor damage nerfs, but they need to be targeted.