The 100 is only needed if you shoot macro.
The 135/2 is like the zoom stuck at 135, you just get the extra stop and a smaller/lighter package.
See a doctor to cure your GAS
Not really. Maybe redundant in focal range but use not so much.
I've sold the 135mm so I may not qualify. Personally, I prefer bokeh from either 85mm or 135mm over the 100mm macro but not by a huge bunch. All three are fine lenses with great IQ, color and sharpness. But they aren't the 70-200mm. Like others this is my workhorse, it's just so good that nothing really compares. But it's heavy as all get-out and as with the big whites, somewhat intimidating. For this reason a smaller, lighter portrait lens with some decent reach is always a good thing to have around. Because of its versatility the 100mm macro is a tough lens not to own in my opinion, but if you aren't interested in tiny things then the alternatives are probably better.