Positions of M.D. and P.D. came about from the bribery scandals of the late 1950s. .
No, they did not.
The positions existed long before "music radio" started in the early 50's. A "music director" was a record librarian, and responsible for organizing the record library and providing the recorded songs needed for each show that had recorded music.
The "bribery scandals" you refer to were shown to be only a few cases, in the late 50's, of "payola" among a few disk jockeys, the most famous being Alan Freed. There were investigations of people like Dick Clark, but they generally went nowhere.
Except at some very big and famous stations... KHJ, CKLW, WMMS and the like, the "Music Director" was just one of the DJs who assisted the PD in dealing with the often-annoying record promoters, getting the "new stuff" together for a weekly music meeting and tasks like getting the "adds" carted and in the studio or replacing "burnt" 45s with fresh copies.
If the station did a chart publication for record store distribution, the MD might be in charge of that.
Yes, off and on there were cases of payola... the "stuff" related to Joe Isgro being the most notorious. But the dealing with the promoters, particularly the independents, was generally the responsibility of the PD and... in the case of the "indies" often done with the consent of management.
Having a management position overseeing the playlist added a layer of protection to the station owners. The idea was to (mostly) eliminate the DJ's from the programming process.
DJs were eliminated from music selection very early in the era of music radio; generally where a DJ played their own music was at small stations or on stations where pop music was just played in one daypart or shift. Those Top 40 stations with hitlists had very tightly defined playlists and rotations and the jocks had nothing to do with the selection of currents.
The bribery problem still exists,
And your proof is where?
In general, unless a station plays a lot of currents and is in a larger market and has its playlist monitored, no record promoter even cares what it plays.
We don't have Hamilton and Gavin and FMQB and the rest of the tip sheets any more. Adds can be seen instantly by subscribers to the airplay monitoring service, and any unusual add is going to be noticed instantly.
but radio has greatly reduced influence over music sales. Today, I see as being more a problem in smaller markets were a track may breakout and get noticed.
Few smaller market stations are monitored...
Major companies that monitor radio station playlists and song airplay include
Mediabase, Luminate BDS (formerly Nielsen BDS), Radiomonitor, DigitalRadioTracker (DRT), and WARM. These services use audio fingerprinting to track when and where songs are played, providing data for music charts, royalties, and promotion.
So if your song is added in Flagstaff or Traverse City or Valdosta, it is not going to be noticed anywhere.
As an example, I have programmed in markets as big as Buenos Aires, Lima, Santiago, Bogotá, San Juan, LA, Chicago, Houston, Miami and the like. I did not have a music director at any of those stations. I had very tight controls on when record promoters could visit, and a log of each visit. Promotions involving artists and their labels were always memorialized in a memo or agreement. Complicated promotions got review of the station or group's lawyer.
And... going back five decades... no song got to stay on the air more than a couple of weeks without some kind of research. No positive listener feedback, no airplay. Yes, I had a music committee in each case... a group that represented the demos of the station and/or programming experience that auditioned the songs critically.
But your idea that Music Directors were created to control payola is just not correct.