Here's my opinion (I learned that qualifier from you );
You like the challenge of getting what you consider a great shot, while spending less. That's commendable, and in many areas I'm the same way. But your rhetoric and dogma for low-end/mid-range machines has become a religion you preach, and it blinds you from thinking freely.
You should have titled the thread differently, again in my opinion; "Don't spend lots of money- I, the Great Tex, can show you how to mimic a great machine for a third the money."
And what I hear from you and GC7 is, "Don't bother with SB/DU machines, they can't do as good a job as a $2500 prosumer machine. Buy a more expensive machine from the outset and be happy" That does go against my frugal nature.
I write from a position of having used and rebuilt
dozens hundreds of different machines; SB/DU consumer machines, HX & double boiler prosumer machines, HX, double boiler, lever operated, and even the oddball hydraulic espresso machine.
Other than a convenience factor of the double boiler machines (only applicable if you make many milk based drinks), and the inconvenience of cooling flushes in HX machines (only a problem if not in frequent use), I can report that every machine I've used could make good espresso drinks.
Some were a pain to use - The Cimbali hydraulic group machine was a leaker; I could never get all the o-rings and gaskets sealed. Some were literally a real pain to use - The Rancilio lever machine I worked on irritated my arthritic shoulder enough to convince me that a lever machine would never be my go to device.
Bottom line for me: Any machine capable of being tuned for proper brew temp and brew pressure is capable of making great espresso. The limiting factor is more the operators skill level than the machine's capabilities. My goal is to ensure that SB/DU machines get a fair shake instead of being looked down on by espresso snobs.