200-400 isn't a "short zoom," it's a very useful focal range - just as 100-300 is (or 70-300, or 120-300, to name a few other focal length ranges found in real lenses).A short zoom is a short zoom. 2x is nothing for a zoom and we only really see that sort a range on more exotic lenses like wide angle lenses nowadays. But I didn't say it couldn't be useful. If it couldn't, then prime users would need serious help! Of course, by short I'm not referring to the focal length, but the zoom ratio.
Sigma has a competitive option out for just 2/3 the price, and the only weakness of that lens is the optics. I don't really understand why the 400mm focal length is getting abandoned like this; the 70-300mm L is admittedly a nice lens but it's no replacement for a 100-400.For a lens, optical quality is rather important, at least for the price point it sits at. As much as I love my 100-400L, I wouldn't say no if a truly better replacement came along. But it remains a good lens amongst the Nikon/Sony equivalents.