Your results are interesting. My 1DX is nearly flawless in all of the auto exposure modes. I thought my 1D4's were great. However, the 1DX is even more accurate. I have noticed that my 5D2 tends to be about 1/8 to 1/3 on the under exposed side, which usually produces fully acceptable images. On the other hand, I found the 7D I had, would over expose most images by 2/3 of a stop, to a full stop and a half? So, I guess there are variables in any man made product. However, after owning everything from film models (FT-B, AE-1s, AE-1Ps, A1s, EOS 620 & 630s, EOS-1, EOS-5, EOS-1n and EOS-1Vs) and digital models (EOS 5D, EOS 5D Mk II, EOS 7D, EOS-1D Mk IVs and EOS-1S X), I don't think I am alone in having been extremely satisfied with all of my Canon products and their precise metering.
I've owned Canon SLR/DSLRs since the '70s and have always found Canon's metering to be outstanding. In fact, while working partime as a NASCAR photog (1998-2001) my shots were chosen over those from my fellow photog's, primarily because of my accurate exposures (Provia 100F film, with less than 1/3 stop of exposure latitude). I never told them I relied solely on the camera's auto metering. Almost everyone (Pro race photogs) in those days used handheld meters and shot manual exposures. I trusted my equipment (EOS-1n & EOS-1V) and knew how accurate their metering was. With the quickly moving subjects and constantly changing lighting conditions at most races, my exposure (and focus) "hit rate" was far greater than most of the other folks I worked with. And that included almost everyone using top-of-the-line Canon and Nikon equipment.