Shield duration is long because damage comes so fast you're often guessing when to shield anyway

E.G.: Rengar ults. When do you shield your AD so they might not die?

...Good question, and if you guess right, you pretty much just got lucky. (Camo duration is 20 seconds at max rank and Rengar will just kill the AD instantly; you cannot react to the Rengar burst.) Shield duration is kind of long to make sure defensive play's reliability in line with offensive play. Nerfing shield duration will just make it really hard for shields to actually do their job. (Also, if a shield's duration is such that you can reasonably wait out said shield, it's probably not doing its job either.)

Maybe shield values are overtuned; I'd buy that one. But nerfing shield duration is ignoring that shielding someone in league often isn't like blocking a reactable overhead in a fighting game or something; you can't see the damage and shield in time and pat yourself on the back. It's not a reaction check. You are actually literally just making a (hopefully informed) guess, and you already pay dearly if you're wrong.

Don't think this is the right direction.