I would not worry about the stitching between the polycarbonate frame and the slide fastener filamentary material (the teeth of the zipper).
The design of carry-on luggage typically includes planning factors of weight, not to exceed 40-50 lbs.
I would never load trollies past 80% of their capability, just to be on the safe side.
The typical airline carrier has an on-board weight limit of 20 lbs.
Most, if not all, airline carry-on designed luggage can hold 20 lbs.