I bought the 100L just recently because I like the fun/challenge of finding interesting macro subjects, but also it doubles as a great portrait lens. This thing is insane wide open on my 5D3 at 2.8 and only gets better as I stop down. My 24-70L Mk1 hasn't been on my camera for a while. The IS is nice and the lens has actually taught me to use MF instead of AF.
I'm curious, just because I don't know any better, why those like Neuro, would take the 135 or 200 f/2 w/o IS at that focal length over something with it?