But 50/50 would be effectively the same meaning as 20/20.
(20/20 means "person being tested sees as well at 20 feet as standard vision at 20 feet.")
(20/20 means "person being tested sees as well at 20 feet as standard vision at 20 feet.")
This isn't obvious; consider that having 3,000/3,000 vision ("I can't read text all that well when it's half a mile away") says pretty much nothing about how clearly you can see things that are 20 feet away.
Nearsightedness and farsightedness are both characterized by "normal vision" at certain distances which becomes markedly worse at certain other distances.
3,000 feet is quite different (for one thing, atmospheric effects start becoming relevant).