"Everybody" who says it's a "great finder" obviously prefer more eye-relief over magnification.
It "seemed" smaller because it optically is.
I never implied otherwise. Of course it is smaller. My point is that when I compared the F3 versus the F3HP, it seemed "smaller but just fine, though." In other words, that the magnification (0.75X) was still good enough for focusing, framing, composing, etc.
You speak about a tradeoff of eye relief vs magnification, but there is another parameter - brightness. And, if the focusing screen stays the same, bigger viewfinder will imply less brightness. Of course, a brighter focusing screen may alleviate this problem, BUT there is ANOTHER problem: engineers can increase focusing screen brightness but in detriment of focusing precision. Of course this assumes the focusing screen technology is the same. 1960s focusing screen technology can't be compared with 1980s technology and so on.
So, all in all, my point is, I wouldn't worry too much about viewfinder magnification, and find 0.75X enough.
Finally, all this debate about Nikon F3's 0.75X versus the OM-1 and it's overhyped 0.92X magnification is child's play once you get accustomed to the viewfinder of a 6x6 or 6x7 camera -- huge, bright, and precise.
BTW, regarding the Nikon F3, for me the location, size, and clarity of the LCD display left to be desired. I sold my F3 due to this and other reasons, the main reason being called "Canon F-1N".