A fun fact about modern strength machines is that if you look at the wheel of the machine, it is often out of round. This is to match the natural strength curve that your body has. So the load is actually variable depending on where you are in the ROM of the rep.
Quad/Hip imbalance is fairly complicated. Both the quads and the hamstrings cross the knee joint as well as the hip. So you need to consider the function of both joints and all the muscles surrounding, not just the hamstrings and quads. Condensing this subject down as best I can; We sit on our ass too much. Our hips and knees are held constant at 90 degrees for. This is compounded with sleeping posture as well, many people sleep on their side, in a position that mimics sitting in a chair, that's where the muscles are comfortable. All of this causes some muscle to become short and tight (quad/calf), some muscles to be loose and long.Your ass muscles and core becomes lazy and inactive. Extra stress is placed on the spine and hamstrings making them injury prone.
There are pros/cons to every exercise. The only machines I tend to lead clients away from are the leg extension/leg curl. Isolation machines are great for aesthetic training, but if your goal is performance and health there are better uses of your time and energy.
I sponsor the local ski teams, they train out of my gym. They bring their own trainer but I've been their while they are working out a fair bit. They do use the leg press, specifically with the alpine racers. The freestyle guys are just goofing around for the most part. If I was training a ski racer, I would use the leg press to train lactic threshold. High volume, moderate weight, rep range shortened, pumping the quads until the burn is too much. Basic barbell training for their base strength, followed by lots of single leg exercises, plyometrics and body weight training.
If you are looking for a good posterior chain exercise, start with hamstring curls on a stability ball. Keep your hips up and don't let them fall. This forces your glutes to stabilize the hip. If you can perform this exercise sucessfully, you can try single leg versions. Then move on to assisted glute ham raises and then unassisted glute ham raise.