This may be different now but back when I mained RNG a few months ago, the charged shot does NOT stack with the DoT ticks of the poison shot. Charge shot does increase the damage on the initial hit though, which makes it deceiving. I did it that way for a long time before I tested it on training dummies a bunch. It’s certainly worth noting the DPS buff globes DO increase the DoT tick damage though.
So in my experience the best soloing opener is to use charged piercing arrow from max distance, land a few more, then poison arrow while at globe cap. Just keep firing away and charge your piercing arrow again as the CDs on those two things are nearly, if not, identical. So it flows very well to use those two in conjunction because piercing arrow is straight damage, so you’ll get the full benefit of the charge that way and much more DPS than what the initial hit on poison arrow will give.
You’ll have to take a hit or two because you can’t trap a mob while poison is still on them, but the moment it wears off throw down the trap, then tele towards the direction the mob came from so you don’t de-aggro. Then repeat your opener from a distance. You can take down impossible (star) level creatures all day like this with ease.
I must reiterate that I haven’t played on RNG much between the last few patches, so perhaps this information is no longer accurate. And this doesn’t take into account any of our new toys as of yesterday. But test out the poison arrow and charge shot combined effects vs. non charged shot and see what you find! Best of luck to you and enjoy it!