Authoritative, or not, here is the latest info from bobistheoilguy.com about Proline:
“The Pro line oil and the QS oil both have a “G” on the bottom of the bottle. They both have the same type of date code cast into the bottom of the bottle as well. I’m assuming that they both come from the same plant.”
That would lead me to believe it is probably a Quaker State product, and I would have no problems using it if it is SL or SM rated oil.
As to being better than Firestone or Walmart bulk, in this neck of the woods, Walmart uses Pennzoil conventional bulk oil (yellow bottle retail) and Firestone stores were using Kendall branded bulk oils. I don’t believe there is a major difference in the oils, because I think they are all SM or SL rated. To me the API SM or SL classification is most important since those are fairly high standards to meet for oils, anyway.