I am wonderring if you can replicate the situation, if yes, compare them with 100mm L (just rent it if you don't have one). I shoot both boxing and wedding. For boxing 135 at f2 and 85l both 1.2 and 2 work and I get above 80% keeper on 5d MK iii. I struggled too during wedding dances. It is darker. I tried the 100mmL macro and it performs much better.
Interesting, looking at the 100L performance on 6d I really didn't expect that as the macro lens af speed is crawling slow. On the other hand, this might be the very reason it performs ok in difficult situations vs. standard lenses like 135L? The 85L seems to have to move too much glass to be a fast af performer.