Gary, ... the only time frame you mention when talking about your worldwide travels is in the '50's when you were in the Mediterranean area ... I would assume that your other travels were somewhere in a 15 - 20 year time frame from then ...
I would first differentiate between a OMB and a soloist ... I consider a OMB a person who is trying to emulate a duo, trio, or full band by means of a drum machine, AKB, backing tracks on a laptop, whatever, whereas a soloist is a person who plays an instrument and perhaps sings ...
I feel the OMB entertainers - as I describe them - is a fairly new 'phenomenon' brought about by the influx of DJs and the reduction, for a variety of reasons, in the number of venues offering live music ... If I were 'traveling the world' 40 or 50 years ago I would not have expected to see OMBs as I don't think they existed as they do today ...
However, since 2005, Lydia and had the good fortune of traveling to Italy twice, and have taken a European cruise and a few cruises to Bermuda ...
I can tell you that during our Italy travels we saw a number of OMBs - primarily KB players using styles or backing tracks and guitar and piano players using backing tracks, mostly off a laptop ... most of them were quite capable artists - of course there were a couple that were not ...
On the cruise ships there were a few KB players in small combos who also used their KB with styles or backing tracks when playing solo gigs during the day ...
If we think about it, how many AKBs were there 35 to 40 years ago and how many were being used as OMB entertainment?

So I think if you were to travel to those same locations today you just MIGHT be surprised at how many OMBs you would see ...

The times, they have a'changed ...