The thinking is that some PG helps the concentrate mix with all the other components thereby increasing the flavour. Most concentrates are in a PG base for this very reason. Another thing that helps a mix flavour is steeping (i.e. time) .... this allows for oxidisation and also allows the components to come together.
Flavour can also change depending what delivery system you are using .... drippers and some tanks have a reputation for delivering more flavour than others.
The last point is that the vape temperature coupled with the delivery system changes flavour ... too cool and too little airflow will lessen flavour because you're producing too little, un-saturated, vape.