The car can sit on its roof upside down and the roof metal all comes together at the pillars/pinch weld there...
If you could spread the load over the length of the gutter, ~ the weight of the car if the rack is rigid enough to hold shape/bear the weight exactly straight down and tight to the edge of the roof/inner edge of the drip rail?
That's far from an engineer stamp approved answer, but no dents/long term damage likely just transferring it through the pillars sitting there in the wind...enough that the car would be un-drivable really as a tipping/cargo loss hazard, even if it didn't dent/damage the roof/bend anything?
That said, over a padded 6-8" roof rack foot x4 even located at the weakest points?
However daring you want to be loading your ~1" yakima sized round pipe/thule 1"x1.5" rectangle shaped bars/the roof rack brackets / bars of your choice up to the task for the most part and can secure it such that it won't fly off during an emergency lane change?
Once you have 2-600lbs on the roof even as low profile/spread/balanced as possible with sufficiently strong brackets/bars, the car should be plenty sketchy/deadly to drive before the drip rails bend/buckle...squashed springs, overburdened/underdamped shocks/scary tire sidewalls, possible roof rack collapse/cargo loss, tippy/scary...potential for denied insurance claims/personal injury/gross negligence/reckless endangerment citations/lawsuits even if nothing happens to you (health/injury/property loss wise as a direct action to you)?
Worry about something besides the drip rails themselves as the constraint?
What are you envisioning that's > 220lb?
Pop top tent/camper contraption?
I had what I calculated was ~500# of oak floor up there once & got a flat tire.
No signs of drip rail issues.
Just a very white knuckle drive/change your underwear if any minor/probable thing happens (gusts of wind, some traction loss, off camber corner, flat tire).
Drove in the slow lane on the full size spare with no traffic in good weather (windy if anything) a short distance home, that was plenty.