Light stun is a bad and annoying design

The frustration of being light stunlocked despite wearing 2 Anti-stun charms is immeasurable. Something is not adding up. Occasionally you get swarmed and maybe stuck on terrain and you get hit, according to my charm I should have nearly 4 seconds of stun protection after one charm charge is triggered, but I die unable to move or act before the 2nd charge even has a chance of getting triggered, I can use my flasks until they're empty or can't keep up and then die, but no other action or movement is possible

The common misunderstanding is that 'Stun Immunity' works just like Freeze/Poison/Bleed Immunity. While they do technically function the same, there is a mechanic unique to Stun called Stun Recovery that sets it apart in practice. Stone Charm makes the application of new Stuns impossible for its duration. It does nothing to affect your character's Stun Recovery.

This effectively makes it so that the initial stun that procs your charm will have its full effect. Because of this, the duration of your true immunity to action interuption via Stun is actually the Stone Charm's duration - your Stun Recovery.

If 2 charms is not enough to mitigate your Stun problems, then your character's Stun Threshold+Recovery is simply too low.

Are you running Chaos Inoculation?

I went unwavering this weekend and man what a difference, forget you stun (and Dodge roll)