Well after 5 pages we seem to be no nearer solving the issue. Before you did the test you describe in your original post, how did you focus your negs? It sounds as if eyeballing focus was only done and discovered to be the best when you did the test. Previously I presume you used one of your focusers at random. That is you simply picked one up and focused a normal neg then printed it. Did you stick with the same focuser for all of a particular printing session or stick with the same focuser each time you print and ignore the other focusers?
In examining your previous normal neg prints I presume you weren't aware of a lack of focus when examining the prints and your decision to conduct the experiment was simply curiosity that arose as a result of deciding to try two focusers on the same neg quite by chance? If you had not done this then I assume you would have been quite satisfied with the prints you had previously produced.
If eyeballing is better and for some reason in your case it is, then I presume that until you did the experiment all your previous prints were judged to be OK with focusers until out of curiosity you tried two focusers one after the other and discovered a difference which led you to try eyeballing as well which was then the best method.
If you examine previous prints that I presume you thought to be OK before your experiment and do them again with eyeballing then can you make them visibly sharper in every case?
As you will have noted one of my thoughts was that the neg in question was in fact out of focus. I had this happen to me and produced a print that was fuzzy despite being able to focus the grain sharply. I had to examine the neg under a big magnifier to see that it was out of focus. It wasn't easy to see this even with a 6x6 neg and a big magnifier.
I then tried to improve things with eyeballing and was able to make a slightly better print but I think I was able to do this because the grain focuser was so sharp compared to my eye that in effect the grain focuser was simply sharpening the "out of focus" neg and making the out of focus clearer