I'm sorry that you did not have good experiences with a Mariposa. I have to wonder if the pack was the wrong size, poorly loaded or adjusted, or some other porblem. I've used a Mariposa for years. I usually keep my pack weight lower, but did take off with 7-8 days worth of food and medications, plus 3 L water. My pack was close to 33 pounds. Not the best, but it carried OK. A few miles in, I added another 2 L of water (next reliable source was very far away.) I was not happy with the weight on my knees, but my back was OK.
Your mileage obviously varied.