Not "wonderful" per se, just a shorthand for all the features, over small capacity, smaller cartridges, other trigger systems, etc. A lot of these 9mm, double-column, selective double-action guns came out at the same time, specifically to address military and police markets open to replacing older pistols or revolvers.
Lived through this time person, and while there were plenty of derogatory terms ("crunchenticker" for the DA pull... which is somehow okay in a revolver?) I have never heard any such attribution to the term wonder nine.