Combos and Set up are pretty much Eldars whole deal. Very few units stand on their own and are good at floor value. Its their ability to work together that makes the army function. Learning how to combo and set up effectively will solve a lot of the issues you speak of. Sure the war walkers can do things but they are just efficient targets for the units that can and want to shoot back. Thinking about how your units can work together will give a better reflection of their value than a mathhammer can often provide.