Another never mentioned factor regarding the number of pleats argument is this.
If Filter A has twice the pleats of Filter B but A filters to 25 Microns on the first pass versus 15 Microns first pass on Filter B then which one is more efficient?
And yes, I remember oil bath air filters. One of my antique Harleys has an oil bath on it. Civilian models used a plain copper mesh. Military used an oil bath with paper cartridges to boot.