Raptor is a breakthrough engine. If NASA with nation state resources and 23B is 6 years late, let’s cut SpaceX some slack for building a profitable launch business with multiple successful vehicles while also being very close with Starship.
> As of 2019, only three full-flow staged combustion rocket engines had ever progressed sufficiently to be tested on test stands; the Soviet Energomash RD-270 project in the 1960s, the US government-funded Aerojet Rocketdyne Integrated powerhead demonstration project in the mid-2000s,[6] and SpaceX's flight capable Raptor engine first test-fired in February 2019.
https://en.wikipedia.org/wiki/Staged_combustion_cycle
If you want to learn more