Great post, Rey.
The weak point you indicated in your kite is the same area I see more in 3-strut kites than 5-struts, especially when boosting.
The pressure situation with your bladder is a challenge. Because the tension on the wall equals the pressure times the radius (LaPlace's Law), you can't put as much pressure in a kite with a fatter leading edge. However, a fatter leading edge gives more support, so there's a trade-off. Perhaps making the leading edge fatter at the weak points, but keeping it the same elsewhere would help.
How about reinforcing the leading edge at the weak points with a baton like in a sail? It would add minimal weight, although it would make storage less optimal.