Yeah, I do that ..... after shaking I let the bubbles rise to the top, then give the bottles a series of little squeezes .... kind of a "Out with the bad air, in with the good" deal for two or three times to allow for the juice to "out gas" the nastiness.
I KNOW Sooner says his juice uses some alcohol based flavorings, but I have to say, I've got over 20 bottles from Lucky 7, and not one of them have that nasty chemical or perfume smell that I'm used to getting with custom mixed juices. Granted, my experience only covers maybe 5 or 6 different companies, but I had gotten to believe that the nasty initial chemical/perfume smell was the norm for pre-steeped juice.
Ah-Grasshopper "Wax on Wax off" or is that "Out with the Old in with the Good". Kind of a pain in the backside.
I know of the chemical smells and taste you mention. I have noticed it in store bought "Off the shelf" juices and some on-line purchases. I have also found it very hard if not impossible to get rid off. These are also the juices that give me a fit of the thirsties.
Actually I haven't noticed much change with age or shaking with the L7 juice. It is pretty good out of the mail box and does get a little more mellow (better) with time. For me I have no qualms about using it from day one.
I did see you mention your Peanut Cup was better at lower power levels. I have seen some people hear talking about 10 to 15 watts. I don't know how they do that and not just cremate their tongues. If I go much above 7 watts everything starts to taste burnt. Which is one of the flavors that my ancient taste buds can still taste [strange irony now that I think about it].
Actually depending on what atty I am using I run from 5.5 to 7.5 watts MAX. Also my buds have a similar history as yours 50 plus years of around two packs a day so my buds take some strong flavor concentrations to get them to even wake up or maybe I should say "resurrect form the dead".