Very true, all about personal preference, opinion and task at hand. The 100-400L is probably the best zoom lens that canon makes, hands down (70-200 f/4 is a close second). I've been impressed with that lens from day one. I had it for last season shooting NHL indoor and man, even if I suffered at ISO1600, those images were tack sharp wide open at all focal lengths. Sharper than my 70-200 2.8 IS. I wished I had kept it, but I didn't feel like sacrificing my 300 2.8 for it. I might pick up another 100-400 for next spring again.
The 14 L is a decent lens and works pretty well, but at 1:1 pixel, its not as sharp as you'd expect a prime to be. There's also some other minor problems with IQ, bust most of them can be easily fixed in PS. Personally for 2k, I wished canon had either made it faster or actually made it a zoom lens. Now the 14 L II is a different beast and really corrects most of the original's faults, but again, the price tag is quite high.
I mean Nikon has a 12-24 f/2.8 zoom lens that kicks the 14 L and 16-35 L out of the water for only 1800ish. And the IQ and sharpness is amazing, even on FF.