Initial designs in the 1930's were zero deflection - just like Del-A-Lum. Only problem was that they had to be periodically greased, which is a pain - even with grease fittings. The ride was also a bit harsh.
Rubber was implemented to solve the problem. You could install it and never worry about greasing it. It had its disadvantages, too, though...rubber deflected a lot more than the steel did, and it had a limited lifespan.
Polyurethane came about as a compromise - nearly zero deflection, long lifespan, and no need for periodic greasing. This had one drawback - squeaking.
Polygraphite, honestly, is the best solution out there. It's graphite impregnated, so there are NO squeaks. Almost zero deflection - meaning it performs extremely close to as well as a solid-design bushing, such as the Del-A-Lum. No need for periodic maintenance - no greasing after the install - ever. And it will last as long as your car will.
Del-A-Lums definitely provide incredible performance. So did the steeling bushings 70 years ago.
Polygraphite is almost zero deflection, and are one less reason that you have to crawl underneath your car.