Even if you just look at the ages of Mo and Gibson (with Mo being younger by seven years but starting her career earlier) then you would say that Mo would've been able to beat Althea in 56-58.
Althea is 15 years older than Marg. When Mags was good enough to win Wimbledon she was 21 and Althea would've been 36.... so it was two champs just missing each other... (similar to Court and Navratilova - they did manage one or two matches against each other) But in their prime as you say it would've been great.
Many people say that a contrast in styles is needed for a great rivalry or exciting match. Not all the time. Gibson and Court played similar and I would've loved to see that one.
Evert and Connolley
Evert and Hingis
Wills and Connolley
Court and Navratilova
Goolagong and Beuno and Mandlikova... are other examples
There's more to life than just being happy.