Hello Dikki
You are quite correct as usual in the Solo/Legato modes.
However it was reintroduced in sampled instruments in the 80s by Akai sample producers who realised that by controlling the sound layers by the keyboard (Instead of a single voice, a mixture was added to make up the solo voice) allowed them to produce the effects required.
When the large VST sample sets became available in the early part of the 21st century, scripts were added to achieve the same job, this scripting combined with the amount of samples used in a single voice means that although the Yamaha SA voices are good, they pale in comparison to VST instruments.
As most professionals engineers (And also musicians) use these VSTs for music production, there has been little need for a hardware board to do the same job.
The only reason Yamaha introduced it on there arranger boards, is because they are aimed squarely at the home market, (Where competition is fierce) where a lot of people require a more simple approach, and so by providing this facility Yamaha guarantee massive sales.
Enjoy whatever you play

Bill