At the very least, this article made me understand why my boiler is made from copper, while the cap and attached group are made from brass!
https://dailycoffeenews.com/2019/05/29/ ... -espresso/
Want to talk espresso but not sure which forum? If so, this is the right one.
I found this statement from the article you linked quite revealing.
... In essence, espresso machines have been temperature and pressure profiling for 70 years.
Everything we have built since then has been, in one way or another, trying to duplicate what these early machines did with springs and levers.