It wouldn't have mattered how long copyright is if it wasn't expanded beyond the immediate economic desincentives that it is supposed to address for the most insidious problems it causes. It should be been limited exclusively to the combined right to reproduction and distribution. Yes, that means that I could reproduce the protected work without limit, so long as don't distribute it. Also means that I could distribute the protected work so long as I do only the copies I acquired.

I, like you, through for a while that length was the problem, now I've poked around enough and known about enough actual examples where shorter length wouldn't have prevented the problems that happens with copyright. The content Sony had repeatedly removed from people's libraries was well within copyright term, shorter copyright wouldn't have saved it. What would have saved it is copyright scope that never extended to controlling access to copies already sold