Legitimate criticism of SpaceX fanboys is not "Pooping on the party". People who pretend that this is a ground-up space program, an icon of how private enterprise is always better at everything, need to be educated in the history of spaceflight. I myself could build a car in my garage that is better/faster/cheaper than everything available in decades past. That doesn't mean that I am one iota smarter, better organized or more innovative than the engineers who built those classic cars.
> better/faster/cheaper than everything
So do talking down SpaceX based on that makes no sense.
They kind of did invent full-flow engines though, which were an unattained holy grail of rocketry.
"Staged combustion (Замкнутая схема) was first proposed by Alexey Isaev in 1949. The first staged combustion engine was the S1.5400 (11D33) used in the Soviet planetary rocket, designed by Melnikov, a former assistant to Isaev.[1] About the same time (1959), Nikolai Kuznetsov began work on the closed cycle engine NK-9 for Korolev's orbital ICBM, GR-1. Kuznetsov later evolved that design into the NK-15 and NK-33 engines for the unsuccessful Lunar N1 rocket. The non-cryogenic N2O4/UDMH engine RD-253 using staged combustion was developed by Valentin Glushko circa 1963 for the Proton rocket."
And way down at the bottom of a long engine list spanning more than half a century...
"Raptor—SpaceX LCH4/LOX engine in development, first flown in 2019[19][20]"
(Yes, there are others listed, but SpaceX was first to actually fly something.)
That the IPD was hydrolox and didn't proceed to the point of a full engine, let alone a flight is besides the point.
What you said was: "They kind of did invent full-flow engines though", which is completely false.
And the billions spent on the technologies that allow those engines to exist. SpaceX didn't invent rocket engines. It stands on the shoulders of many giants going back through Apollo to the early days. There are even traces of Soviet tech in the raptor (ie closed cycle). Nearly all of that work was funded by taxpayers ... and by whatever funded the soviet programs.
Building a better mousetrap is great, but that doesn't mean that all the previous mousetraps were not also great too.