I've never seen thicker PG. Different VG's have different viscosity.
Steeping is done with a closed bottle. (Entropy is the target)
Breathe or Airing-Out is an open bottle. (Oxidation, evaporation of high notes and alcohol, adding a bitter taste is the target)
They do two different things to a mix and it is darn shame to confuse them into one concept.
Of the companies you listed, the only one I know that carries VG flavoring is TPA/TFA. (I don't play with FW's stuff, so don't know anything about it.)