You are spot-on, Pete. I remember when mechanical fuel pumps were disassemble-able. When the diaphragm went bad, you could pull it out and replace it. Only it.
I can deluge y'all with stories about people who had their vehicles- or even other stuff- in to the shop for repairs, and it remained broken even after the "mechanics" threw hundreds of dollars worth of new parts at it.
Evidently diagnostic skills are a thing of the past.
XGF's mom had a poor running carbd car. It had the fuel economy of a bus, no power, etc. The local garage threw everything at it- computer, wires... basically replaced the entire ignition system from top to bottom... can you imagine the cost???... and IIRC some fuel system parts too, with no improvement. I said "lemme have a looky-see". Brought it to my place, popped the lid off the carb- didn't even remove the body- pulled the floats out and threw em in a bucket of water. One of them went straight for the bottom. DAH. $4.60 later she had her car back, running better than it had in years.
That's basic stuff Man. BASIC.
