Yes, PG is hygroscopic, but it is also miscible with water. It doesn't matter if PG is in water, the effects can still occur. You are only talking about dilution at this point.
Unfortunately, it's a bit hard to find actual studies of composition of e-liquid, but here is one example of testing of Crown-7 liquid. Among all of the other components, it was found to contain at over 60% PG Wt-%, and over 8% water Wt-%. However, the vapor had over 2% PG Wt-%, and the water was over 66% Wt-%. Granted I don't have numbers for every liquid we vape, because frankly there are a severe lack of studies to provide the results. But based on the above, I don't see how that can be considered hydrated.
I found a couple more that didn't list water at all (though more likely they either were not testing for it, or didn't include it in the list for whatever reason), and one with water content less than 1% in the liquid (no composition of vapor).
