Advice needed, Need a new telelens for my Canon 7D

I had the 400 5.6L, and while it is a great lens, I found a 100-400 that is 95% as sharp wide open and the same at any other aperture. On top of that I got 100-380 (zoom lenses are never really what they say they are) + IS. So I sold the prime.

Supposedly the prime can focus faster, but I never noticed a difference.

I also have a Kenko 1.4X and with taped pins, both the 400mm 5.6L and the 100-400 have AF on the 7D, but the center point is really bad . Side focus points are ok (on the right they are actually better than on the left, for some reason).

I also had the 300 F4L (no IS) and it was fine with the 1.4X kenko, but not as good as the 400 5.6L.

For fast + accurate focus I would stay with Canon lenses.