tompoland essentially he was saying that putting springs into lever machines removed, in large part, the ability to vary the pressure.
It did, unless you purposefully retard the lever. It also makes the assumption that the ability to profile pressure is superior. Over the years, although useful, most profiling ends up looking like a lever profile. The one thing levers do, is fill in a unique way. The more advanced ones are then effectively a PID controlled boiler forming part of the group.
Temperature stability on the generation of new dual boiler levers is rather excellent and there is the ability to produce a declining, falling or rising temperature shot. These are not the levers of the past, where temperature is highly unstable. Starting off super hot, then cooling and for subsequent shots different again from even the one you did previously.
Sure a spring may have impacted the lever of yesteryear in a few ways…not only pressure, but also the ability to control the flow rate of water entering the group! This ability to let water enter slowly could possibly mitigate the effect of very hot water entering the group. Unlike home levers, the commercial manual levers had big boilers and didn’t need to run so hot. Today the most modern levers, rightly, remove the link between steaming and brewing