I don't get the hype about this lens. There is already a 70-300L out, which does have 100mm less, but you can get that with a 1.4x TC for cheaper than this 100-400 is supposed to be.
For every f/2.8 70-200 II owner, this 100-400 lens is just pretty useless.
First, you're blowing away 100mm worth of f/2.8 super high IQ goodness
Then, if you need the reach, just add a TC and you got it with probably similar IQ.
What any 70-200 II owner needs is a 200-400 f/4 and not this rubbish.
If you dont have a tele lens at all, 100-400mm gets you covered nicely in once package, but if you have a 70-200, it's kinda useless.
Uh, no. My 70-200 2.8 II is way too short for wildlife, and the 2.8 is unnecessary the majority of the time outside. The 1.2 TC doesn't add much, and the 2X has other issues as mentioned (there is no free lunch). I keep the 2.8 for indoor events and people photography mostly which is where it shines.
A 100-400 would be the lens I grab as a complement to my nature hikes and photography. A 1.2 will give me 480 - almost 500 which is very usable for birds (especially on a crop body). Plus I can zoom out for some usable landscape photos.
Each has a best application I find the 70-200 doesn't work well as a wildlife lens but a 100-400 would be a perfect complement to my 16-35.
I was hiking around Mohican State Park with my 100-400L lens all day, then had to swing back into Mansfield for a basketball game, where I used the 70-200L lens. So yes, I agree with your usages too, there is simultaneous value.